Merge branch 'jc/filter-commit'

* jc/filter-commit:
  git log: Unify header_filter and message_filter into one.
  Update grep internal for grepping only in head/body
  git-log --author and --committer are not left-anchored by default
  rev-list: fix segfault with --{author,committer,grep}
  revision traversal: --author, --committer, and --grep.
  revision traversal: prepare for commit log match.
  builtin-grep: make pieces of it available as library.

diff --combined Makefile
index 4a8cd22602828cd7ae5efb74a3798b7e641a1b04,b15aa9dbb96b3aa886b196b832c87f46541ceac1..51fbe6aa8287223465c4eee69379f812c7058d61
--- 1/Makefile
--- 2/Makefile
+++ b/Makefile
@@@ -234,7 -234,7 +234,7 @@@ LIB_FILE=libgit.
  XDIFF_LIB=xdiff/lib.a
  
  LIB_H = \
-       archive.h blob.h cache.h commit.h csum-file.h delta.h \
+       archive.h blob.h cache.h commit.h csum-file.h delta.h grep.h \
        diff.h object.h pack.h pkt-line.h quote.h refs.h list-objects.h sideband.h \
        run-command.h strbuf.h tag.h tree.h git-compat-util.h revision.h \
        tree-walk.h log-tree.h dir.h path-list.h unpack-trees.h builtin.h
@@@ -246,17 -246,15 +246,17 @@@ DIFF_OBJS = 
  
  LIB_OBJS = \
        blob.o commit.o connect.o csum-file.o cache-tree.o base85.o \
 -      date.o diff-delta.o entry.o exec_cmd.o ident.o lockfile.o \
 +      date.o diff-delta.o entry.o exec_cmd.o ident.o \
 +      interpolate.o \
 +      lockfile.o \
        object.o pack-check.o patch-delta.o path.o pkt-line.o sideband.o \
        quote.o read-cache.o refs.o run-command.o dir.o object-refs.o \
        server-info.o setup.o sha1_file.o sha1_name.o strbuf.o \
        tag.o tree.o usage.o config.o environment.o ctype.o copy.o \
        fetch-clone.o revision.o pager.o tree-walk.o xdiff-interface.o \
-       write_or_die.o trace.o list-objects.o \
+       write_or_die.o trace.o list-objects.o grep.o \
        alloc.o merge-file.o path-list.o help.o unpack-trees.o $(DIFF_OBJS) \
 -      color.o wt-status.o
 +      color.o wt-status.o archive-zip.o
  
  BUILTIN_OBJS = \
        builtin-add.o \
@@@ -302,7 -300,8 +302,7 @@@
        builtin-upload-archive.o \
        builtin-upload-tar.o \
        builtin-verify-pack.o \
 -      builtin-write-tree.o \
 -      builtin-zip-tree.o
 +      builtin-write-tree.o
  
  GITLIBS = $(LIB_FILE) $(XDIFF_LIB)
  LIBS = $(GITLIBS) -lz