git log --author='Jeff King'

I have three patch series that makes a part of git-grep
available and use it for log filtering:

 [PATCH] builtin-grep: make pieces of it available as library.
 [PATCH] revision traversal: prepare for commit log match.
 [PATCH] revision traversal: --author, --committer, and --grep.

I didn't implement the boolean combination of patterns like
git-grep does, but it should be pretty straightforward to do so
in setup_revisions().  The syntax probably would be something
like:

    git log --grep-( rev-list gitweb --and --not --author=Jakub --grep-)

to find logs that:

 * talk about rev-list, or
 * talk about gitweb but not by Jakub