Strip domain from email address

I work in a company that has changed domain name. Everyone has the same username but the domain in the email has changed. `graf` shows developers in our repos as having two sets of commits -- one with the old domain, one with the new domain. Stripping off the domain is effective for merging these.

I'll admit it would not work if you had two people who had identical usernames and different domains and they really **were** different people. In the general case, though, I think this is an improvement.