Merge branch 'jk/interop-test'

Picking two versions of Git and running tests to make sure the
older one and the newer one interoperate happily has now become
possible.

* jk/interop-test:
t/interop: add test of old clients against modern git-daemon
t: add an interoperability test harness

diff --combined Makefile
index ed68700acb19bfe1f24e3143200baf112dd5a7dd,7156b051e7aea7019b573b3633a24dcb5e5f475e..ba524f3a7819db3ce2347cd76781b99241539735
--- 1/Makefile
--- 2/Makefile
+++ b/Makefile
@@@ -102,6 -102,8 +102,6 @@@ all:
  #
  # Define MKDIR_WO_TRAILING_SLASH if your mkdir() can't deal with trailing slash.
  #
 -# Define NO_MKSTEMPS if you don't have mkstemps in the C library.
 -#
  # Define NO_GECOS_IN_PWENT if you don't have pw_gecos in struct passwd
  # in the C library.
  #
@@@ -779,7 -781,6 +779,7 @@@ LIB_OBJS += notes-cache.
  LIB_OBJS += notes-merge.o
  LIB_OBJS += notes-utils.o
  LIB_OBJS += object.o
 +LIB_OBJS += oidset.o
  LIB_OBJS += pack-bitmap.o
  LIB_OBJS += pack-bitmap-write.o
  LIB_OBJS += pack-check.o
@@@ -931,7 -932,6 +931,7 @@@ BUILTIN_OBJS += builtin/prune.
  BUILTIN_OBJS += builtin/pull.o
  BUILTIN_OBJS += builtin/push.o
  BUILTIN_OBJS += builtin/read-tree.o
 +BUILTIN_OBJS += builtin/rebase--helper.o
  BUILTIN_OBJS += builtin/receive-pack.o
  BUILTIN_OBJS += builtin/reflog.o
  BUILTIN_OBJS += builtin/remote.o
@@@ -1280,6 -1280,9 +1280,6 @@@ ifdef MKDIR_WO_TRAILING_SLAS
        COMPAT_CFLAGS += -DMKDIR_WO_TRAILING_SLASH
        COMPAT_OBJS += compat/mkdir.o
  endif
 -ifdef NO_MKSTEMPS
 -      COMPAT_CFLAGS += -DNO_MKSTEMPS
 -endif
  ifdef NO_UNSETENV
        COMPAT_CFLAGS += -DNO_UNSETENV
        COMPAT_OBJS += compat/unsetenv.o
@@@ -2251,6 -2254,9 +2251,9 @@@ endi
  ifdef GIT_PERF_MAKE_OPTS
        @echo GIT_PERF_MAKE_OPTS=\''$(subst ','\'',$(subst ','\'',$(GIT_PERF_MAKE_OPTS)))'\' >>$@+
  endif
+ ifdef GIT_INTEROP_MAKE_OPTS
+       @echo GIT_INTEROP_MAKE_OPTS=\''$(subst ','\'',$(subst ','\'',$(GIT_INTEROP_MAKE_OPTS)))'\' >>$@+
+ endif
  ifdef TEST_GIT_INDEX_VERSION
        @echo TEST_GIT_INDEX_VERSION=\''$(subst ','\'',$(subst ','\'',$(TEST_GIT_INDEX_VERSION)))'\' >>$@+
  endif