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 --cc Makefile
index 4a8cd22602828cd7ae5efb74a3798b7e641a1b04,b15aa9dbb96b3aa886b196b832c87f46541ceac1..51fbe6aa8287223465c4eee69379f812c7058d61
--- 1/Makefile
--- 2/Makefile
+++ b/Makefile
@@@ -254,9 -252,9 +254,9 @@@ LIB_OBJS = 
        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 \