Merge branch 'maint'

* maint:
Update draft release notes for 1.6.0.1
Add hints to revert documentation about other ways to undo changes
Install templates with the user and group of the installing personality
"git-merge": allow fast-forwarding in a stat-dirty tree
completion: find out supported merge strategies correctly
decorate: allow const objects to be decorated
for-each-ref: cope with tags with incomplete lines
diff --check: do not get confused by new blank lines in the middle
remote.c: remove useless if-before-free test
mailinfo: avoid violating strbuf assertion
git format-patch: avoid underrun when format.headers is empty or all NLs

diff --combined diff.c
index 10d54405d21888d41a1e20f27358e15ba5b679d5,f70e6b4912911bd3f3a1d385fce7119a4a8107f6..5923fe281b6ab421f785a1d47afd6dee5711e52d
--- 1/diff.c
--- 2/diff.c
+++ b/diff.c
@@@ -20,7 -20,6 +20,7 @@@
  
  static int diff_detect_rename_default;
  static int diff_rename_limit_default = 200;
 +static int diff_suppress_blank_empty;
  int diff_use_color_default = -1;
  static const char *external_diff_cmd_cfg;
  int diff_auto_refresh_index = 1;
@@@ -177,12 -176,6 +177,12 @@@ int git_diff_basic_config(const char *v
                return 0;
        }
  
 +      /* like GNU diff's --suppress-blank-empty option  */
 +      if (!strcmp(var, "diff.suppress-blank-empty")) {
 +              diff_suppress_blank_empty = git_config_bool(var, value);
 +              return 0;
 +      }
 +
        if (!prefixcmp(var, "diff.")) {
                const char *ep = strrchr(var, '.');
                if (ep != var + 4) {
@@@ -376,6 -369,7 +376,6 @@@ static void diff_words_append(char *lin
  }
  
  struct diff_words_data {
 -      struct xdiff_emit_state xm;
        struct diff_words_buffer minus, plus;
        FILE *file;
  };
@@@ -465,8 -459,11 +465,8 @@@ static void diff_words_show(struct diff
  
        xpp.flags = XDF_NEED_MINIMAL;
        xecfg.ctxlen = diff_words->minus.alloc + diff_words->plus.alloc;
 -      ecb.outf = xdiff_outf;
 -      ecb.priv = diff_words;
 -      diff_words->xm.consume = fn_out_diff_words_aux;
 -      xdi_diff(&minus, &plus, &xpp, &xecfg, &ecb);
 -
 +      xdi_diff_outf(&minus, &plus, fn_out_diff_words_aux, diff_words,
 +                    &xpp, &xecfg, &ecb);
        free(minus.ptr);
        free(plus.ptr);
        diff_words->minus.text.size = diff_words->plus.text.size = 0;
@@@ -480,6 -477,7 +480,6 @@@
  typedef unsigned long (*sane_truncate_fn)(char *line, unsigned long len);
  
  struct emit_callback {
 -      struct xdiff_emit_state xm;
        int nparents, color_diff;
        unsigned ws_rule;
        sane_truncate_fn truncate;
@@@ -582,12 -580,6 +582,12 @@@ static void fn_out_consume(void *priv, 
                ecbdata->label_path[0] = ecbdata->label_path[1] = NULL;
        }
  
 +      if (diff_suppress_blank_empty
 +          && len == 2 && line[0] == ' ' && line[1] == '\n') {
 +              line[0] = '\n';
 +              len = 1;
 +      }
 +
        /* This is not really necessary for now because
         * this codepath only deals with two-way diffs.
         */
@@@ -716,6 -708,8 +716,6 @@@ static char *pprint_rename(const char *
  }
  
  struct diffstat_t {
 -      struct xdiff_emit_state xm;
 -
        int nr;
        int alloc;
        struct diffstat_file {
@@@ -1137,6 -1131,7 +1137,6 @@@ static void free_diffstat_info(struct d
  }
  
  struct checkdiff_t {
 -      struct xdiff_emit_state xm;
        const char *filename;
        int lineno;
        struct diff_options *o;
@@@ -1526,13 -1521,15 +1526,13 @@@ static void builtin_diff(const char *na
                        xecfg.ctxlen = strtoul(diffopts + 10, NULL, 10);
                else if (!prefixcmp(diffopts, "-u"))
                        xecfg.ctxlen = strtoul(diffopts + 2, NULL, 10);
 -              ecb.outf = xdiff_outf;
 -              ecb.priv = &ecbdata;
 -              ecbdata.xm.consume = fn_out_consume;
                if (DIFF_OPT_TST(o, COLOR_DIFF_WORDS)) {
                        ecbdata.diff_words =
                                xcalloc(1, sizeof(struct diff_words_data));
                        ecbdata.diff_words->file = o->file;
                }
 -              xdi_diff(&mf1, &mf2, &xpp, &xecfg, &ecb);
 +              xdi_diff_outf(&mf1, &mf2, fn_out_consume, &ecbdata,
 +                            &xpp, &xecfg, &ecb);
                if (DIFF_OPT_TST(o, COLOR_DIFF_WORDS))
                        free_diff_words_data(&ecbdata);
        }
@@@ -1583,8 -1580,9 +1583,8 @@@ static void builtin_diffstat(const cha
  
                memset(&xecfg, 0, sizeof(xecfg));
                xpp.flags = XDF_NEED_MINIMAL | o->xdl_opts;
 -              ecb.outf = xdiff_outf;
 -              ecb.priv = diffstat;
 -              xdi_diff(&mf1, &mf2, &xpp, &xecfg, &ecb);
 +              xdi_diff_outf(&mf1, &mf2, diffstat_consume, diffstat,
 +                            &xpp, &xecfg, &ecb);
        }
  
   free_and_return:
@@@ -1605,6 -1603,7 +1605,6 @@@ static void builtin_checkdiff(const cha
                return;
  
        memset(&data, 0, sizeof(data));
 -      data.xm.consume = checkdiff_consume;
        data.filename = name_b ? name_b : name_a;
        data.lineno = 0;
        data.o = o;
@@@ -1628,9 -1627,11 +1628,10 @@@
                xdemitcb_t ecb;
  
                memset(&xecfg, 0, sizeof(xecfg));
+               xecfg.ctxlen = 1; /* at least one context line */
                xpp.flags = XDF_NEED_MINIMAL;
 -              ecb.outf = xdiff_outf;
 -              ecb.priv = &data;
 -              xdi_diff(&mf1, &mf2, &xpp, &xecfg, &ecb);
 +              xdi_diff_outf(&mf1, &mf2, checkdiff_consume, &data,
 +                            &xpp, &xecfg, &ecb);
  
                if ((data.ws_rule & WS_TRAILING_SPACE) &&
                    data.trailing_blanks_start) {
@@@ -3018,6 -3019,7 +3019,6 @@@ static void diff_summary(FILE *file, st
  }
  
  struct patch_id_t {
 -      struct xdiff_emit_state xm;
        SHA_CTX *ctx;
        int patchlen;
  };
@@@ -3062,6 -3064,7 +3063,6 @@@ static int diff_get_patch_id(struct dif
        SHA1_Init(&ctx);
        memset(&data, 0, sizeof(struct patch_id_t));
        data.ctx = &ctx;
 -      data.xm.consume = patch_id_consume;
  
        for (i = 0; i < q->nr; i++) {
                xpparam_t xpp;
@@@ -3126,8 -3129,9 +3127,8 @@@
                xpp.flags = XDF_NEED_MINIMAL;
                xecfg.ctxlen = 3;
                xecfg.flags = XDL_EMIT_FUNCNAMES;
 -              ecb.outf = xdiff_outf;
 -              ecb.priv = &data;
 -              xdi_diff(&mf1, &mf2, &xpp, &xecfg, &ecb);
 +              xdi_diff_outf(&mf1, &mf2, patch_id_consume, &data,
 +                            &xpp, &xecfg, &ecb);
        }
  
        SHA1_Final(sha1, &ctx);
@@@ -3204,6 -3208,7 +3205,6 @@@ void diff_flush(struct diff_options *op
                struct diffstat_t diffstat;
  
                memset(&diffstat, 0, sizeof(struct diffstat_t));
 -              diffstat.xm.consume = diffstat_consume;
                for (i = 0; i < q->nr; i++) {
                        struct diff_filepair *p = q->queue[i];
                        if (check_pair_status(p))