Careful with keys.
Careful with keys.

@jdcasey reported this.

It seems that github.com is sending a new or modified message type that has a
`committer` field in the commit, but with no `username` field.  It instead has
a `user`.  We were raising `KeyError` exceptions when these got sent.

This should treat those messages more carefully.

fedora-infra/github2fedmsg,fedora-infra/github2fedmsg