Fix cvs2git branch handling

Fix cvs2git branch handling

.. and tell 'co' to shut up about the rcs noise.

This still leaves some branch issues up in the air: it looks like
cvsps has some questionable originating branch information, but I
don't know whether that's a cvsps bug or an actual bug in the
syslinux archive I'm using to test.

I'll let David Mansfield answer my questions about CVS. I'm a
total idiot when it comes to branches under CVS ("I'm pure!").