git-gui: Handle progress bars from newer gits

git-gui: Handle progress bars from newer gits

Post Git 1.5.3 a new style progress bar has been introduced that
uses only one line rather than two.  The formatting of the completed
and total section is also slightly different so we must adjust our
regexp to match.  Unfortunately both styles are in active use by
different versions of Git so we need to look for both.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>