Try to guess the user's name and email

Try to guess the user's name and email

A common use case for RCS fast export is likely to be of a user trying to
convert its RCS histories into git histories. In these cases we don't need an
authors file, since the committer full name and email are information likely
to be found elsewhere.

We look at the git config, but also the gecos entry in the passwd file. As
extreme resources we also peek in their .hgrc and .vimrc files