Apparently do_switch() tolerates the lack of escaping in less
funky branch names.  For the really strange and scary ones, we
need to escape them properly.  It strangely maintains compatible
with the existing handling of branch names with spaces and
exclamation marks.

Reported-by: m.skoric@web.de ($gmane/94677)
Signed-off-by: NEric Wong <normalperson@yhbt.net>