git-push: allow globbing wildcard refspec.

git-push: allow globbing wildcard refspec.

This allows you to set up mothership-satellite configuration
more symmetrically and naturally by allowing the globbing
wildcard refspec for git-push.  On your satellite machine:

    [remote "mothership"]
        url = mothership:project.git
        fetch = refs/heads/*:refs/remotes/mothership/*
        push = refs/heads/*:refs/remotes/satellite/*

You would say "git fetch mothership" to update your tracking
branches under mothership/ to keep track of the progress on the
mothership side, and when you are done working on the satellite
machine, you would "git push mothership" to update their
tracking branches under satellite/.  Corresponding configuration
on the mothership machine can be used to make "git fetch satellite"
update its tracking branch under satellite/. on the mothership.

Signed-off-by: Junio C Hamano <junkio@cox.net>