Merge branch 'ma/doc-diff-doc-vs-doctor-comparison'

Dev support update to make it easier to compare two formatted
results from our documentation.

* ma/doc-diff-doc-vs-doctor-comparison:
doc-diff: add `--cut-header-footer`
doc-diff: support diffing from/to AsciiDoc(tor)
doc-diff: let `render_tree()` take an explicit directory name
Doc: auto-detect changed build flags

diff --combined Documentation/Makefile
index ccac771d3fb5ecb863c64a782a947a76593df397,b534623012daacfd651916b454d2598c9508d9e9..4e4dd7ecf14919fa3d5735daa6b87c8addcff1e8
--- 1/Documentation/Makefile
--- 2/Documentation/Makefile
+++ b/Documentation/Makefile
@@@ -331,6 -331,15 +331,15 @@@ mergetools-list.made: ../git-mergetool-
                show_tool_names can_merge "* " || :' >mergetools-merge.txt && \
        date >$@
  
+ TRACK_ASCIIDOCFLAGS = $(subst ','\'',$(ASCIIDOC_COMMON):$(ASCIIDOC_HTML):$(ASCIIDOC_DOCBOOK))
+ 
+ GIT-ASCIIDOCFLAGS: FORCE
+       @FLAGS='$(TRACK_ASCIIDOCFLAGS)'; \
+           if test x"$$FLAGS" != x"`cat GIT-ASCIIDOCFLAGS 2>/dev/null`" ; then \
+               echo >&2 "    * new asciidoc flags"; \
+               echo "$$FLAGS" >GIT-ASCIIDOCFLAGS; \
+             fi
+ 
  clean:
        $(RM) *.xml *.xml+ *.html *.html+ *.1 *.5 *.7
        $(RM) *.texi *.texi+ *.texi++ git.info gitman.info
@@@ -340,13 -349,14 +349,14 @@@
        $(RM) SubmittingPatches.txt
        $(RM) $(cmds_txt) $(mergetools_txt) *.made
        $(RM) manpage-base-url.xsl
+       $(RM) GIT-ASCIIDOCFLAGS
  
- $(MAN_HTML): %.html : %.txt asciidoc.conf asciidoctor-extensions.rb
 -$(MAN_HTML): %.html : %.txt asciidoc.conf GIT-ASCIIDOCFLAGS
++$(MAN_HTML): %.html : %.txt asciidoc.conf asciidoctor-extensions.rb GIT-ASCIIDOCFLAGS
        $(QUIET_ASCIIDOC)$(RM) $@+ $@ && \
        $(TXT_TO_HTML) -d manpage -o $@+ $< && \
        mv $@+ $@
  
- $(OBSOLETE_HTML): %.html : %.txto asciidoc.conf asciidoctor-extensions.rb
 -$(OBSOLETE_HTML): %.html : %.txto asciidoc.conf GIT-ASCIIDOCFLAGS
++$(OBSOLETE_HTML): %.html : %.txto asciidoc.conf asciidoctor-extensions.rb GIT-ASCIIDOCFLAGS
        $(QUIET_ASCIIDOC)$(RM) $@+ $@ && \
        $(TXT_TO_HTML) -o $@+ $< && \
        mv $@+ $@
@@@ -354,16 -364,16 +364,16 @@@
  manpage-base-url.xsl: manpage-base-url.xsl.in
        $(QUIET_GEN)sed "s|@@MAN_BASE_URL@@|$(MAN_BASE_URL)|" $< > $@
  
 -%.1 %.5 %.7 : %.xml manpage-base-url.xsl
 +%.1 %.5 %.7 : %.xml manpage-base-url.xsl $(wildcard manpage*.xsl)
        $(QUIET_XMLTO)$(RM) $@ && \
        $(XMLTO) -m $(MANPAGE_XSL) $(XMLTO_EXTRA) man $<
  
- %.xml : %.txt asciidoc.conf asciidoctor-extensions.rb
 -%.xml : %.txt asciidoc.conf GIT-ASCIIDOCFLAGS
++%.xml : %.txt asciidoc.conf asciidoctor-extensions.rb GIT-ASCIIDOCFLAGS
        $(QUIET_ASCIIDOC)$(RM) $@+ $@ && \
        $(TXT_TO_XML) -d manpage -o $@+ $< && \
        mv $@+ $@
  
- user-manual.xml: user-manual.txt user-manual.conf asciidoctor-extensions.rb
 -user-manual.xml: user-manual.txt user-manual.conf GIT-ASCIIDOCFLAGS
++user-manual.xml: user-manual.txt user-manual.conf asciidoctor-extensions.rb GIT-ASCIIDOCFLAGS
        $(QUIET_ASCIIDOC)$(RM) $@+ $@ && \
        $(TXT_TO_XML) -d book -o $@+ $< && \
        mv $@+ $@
@@@ -373,7 -383,8 +383,8 @@@ technical/api-index.txt: technical/api-
        $(QUIET_GEN)cd technical && '$(SHELL_PATH_SQ)' ./api-index.sh
  
  technical/%.html: ASCIIDOC_EXTRA += -a git-relative-html-prefix=../
- $(patsubst %,%.html,$(API_DOCS) technical/api-index $(TECH_DOCS)): %.html : %.txt asciidoc.conf
+ $(patsubst %,%.html,$(API_DOCS) technical/api-index $(TECH_DOCS)): %.html : %.txt \
+       asciidoc.conf GIT-ASCIIDOCFLAGS
        $(QUIET_ASCIIDOC)$(TXT_TO_HTML) $*.txt
  
  SubmittingPatches.txt: SubmittingPatches
@@@ -430,7 -441,7 +441,7 @@@ $(patsubst %,%.html,$(ARTICLES)) : %.ht
  WEBDOC_DEST = /pub/software/scm/git/docs
  
  howto/%.html: ASCIIDOC_EXTRA += -a git-relative-html-prefix=../
- $(patsubst %.txt,%.html,$(wildcard howto/*.txt)): %.html : %.txt
+ $(patsubst %.txt,%.html,$(wildcard howto/*.txt)): %.html : %.txt GIT-ASCIIDOCFLAGS
        $(QUIET_ASCIIDOC)$(RM) $@+ $@ && \
        sed -e '1,/^$$/d' $< | \
        $(TXT_TO_HTML) - >$@+ && \