* 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.