From: martin f. krafft <madduck@debian.org>
Subject: [TopGit PATCH] Unify export of branches

Currently, tg-export does things a little differently whether -b is passed or
not, when really -b should just default to the name of the current branch.

-b can also be used with the collapse driver.

Debian bug: #506284
Credits: Niko Tyni <ntyni@debian.org> for spotting the bug and sending an
 initial fix.

Signed-off-by: martin f. krafft <madduck@debian.org>