R1:3ce0c602ec59

Improve Diffusion parser linking of author names

Summary: See T502. Under some VCS setups, we get full email addresses instead of
usernames or real names. Try harder to find matches, by falling back to email
address parsing if we don't get hits on the straight-up token parsing.

Test Plan:
This is difficult to test because it depends on the account state and repository
state, and hard to pull out so it's more testable without better mocking
facilities. I just dumped this into the parser to verify the…