[slimsag]

FWIW you can do this with Sourcegraph today, searching over both diffs (code changes)[0] and commit messages[1]:

[0] https://sourcegraph.com/search?q=context:global+repo:%5Egith...

[1] https://sourcegraph.com/search?q=context:global+repo:%5Egith...

(I work there, just commenting on my own though. we're all pretty happy to have competition, more awareness of code search, etc.)