Merge branch 'ks/tree-diff-nway'

Instead of running N pair-wise diff-trees when inspecting a
N-parent merge, find the set of paths that were touched by walking
N+1 trees in parallel.  These set of paths can then be turned into
N pair-wise diff-tree results to be processed through rename
detections and such.  And N=2 case nicely degenerates to the usual
2-way diff-tree, which is very nice.

* ks/tree-diff-nway:
  mingw: activate alloca
  combine-diff: speed it up, by using multiparent diff tree-walker directly
  tree-diff: rework diff_tree() to generate diffs for multiparent cases as well
  Portable alloca for Git
  tree-diff: reuse base str(buf) memory on sub-tree recursion
  tree-diff: no need to call "full" diff_tree_sha1 from show_path()
  tree-diff: rework diff_tree interface to be sha1 based
  tree-diff: diff_tree() should now be static
  tree-diff: remove special-case diff-emitting code for empty-tree cases
  tree-diff: simplify tree_entry_pathcmp
  tree-diff: show_path prototype is not needed anymore
  tree-diff: rename compare_tree_entry -> tree_entry_pathcmp
  tree-diff: move all action-taking code out of compare_tree_entry()
  tree-diff: don't assume compare_tree_entry() returns -1,0,1
  tree-diff: consolidate code for emitting diffs and recursion in one place
  tree-diff: show_tree() is not needed
  tree-diff: no need to pass match to skip_uninteresting()
  tree-diff: no need to manually verify that there is no mode change for a path
  combine-diff: move changed-paths scanning logic into its own function
  combine-diff: move show_log_first logic/action out of paths scanning

diff --cc Makefile
Simple merge

diff --cc cache.h
Simple merge

diff --cc config.mak.uname
index 23a880365616c34ea84d8a3194b98163864a2cd1,9967de66a2c7f4c52c1f218f434ed8aeb67254b8..97acf8fea630ad47d51567782f5e27661e00006b
--- 1/config.mak.uname
--- 2/config.mak.uname
+++ b/config.mak.uname
@@@ -357,9 -369,9 +363,9 @@@ ifeq ($(uname_S),Windows
        COMPAT_OBJS = compat/msvc.o compat/winansi.o \
                compat/win32/pthread.o compat/win32/syslog.o \
                compat/win32/dirent.o
-       COMPAT_CFLAGS = -D__USE_MINGW_ACCESS -DNOGDI -DHAVE_STRING_H -DHAVE_ALLOCA_H -Icompat -Icompat/regex -Icompat/win32 -DSTRIP_EXTENSION=\".exe\"
+       COMPAT_CFLAGS = -D__USE_MINGW_ACCESS -DNOGDI -DHAVE_STRING_H -Icompat -Icompat/regex -Icompat/win32 -DSTRIP_EXTENSION=\".exe\"
        BASIC_LDFLAGS = -IGNORE:4217 -IGNORE:4049 -NOLOGO -SUBSYSTEM:CONSOLE -NODEFAULTLIB:MSVCRT.lib
 -      EXTLIBS = user32.lib advapi32.lib shell32.lib wininet.lib ws2_32.lib
 +      EXTLIBS = user32.lib advapi32.lib shell32.lib wininet.lib ws2_32.lib invalidcontinue.obj
        PTHREAD_LIBS =
        lib =
  ifndef DEBUG

diff --cc configure.ac
Simple merge

diff --cc diff.c
Simple merge

diff --cc diff.h
Simple merge

diff --cc git-compat-util.h
Simple merge