git-gui: Don't display CR within console windows

git-gui: Don't display CR within console windows

Git progress bars from tools like git-push and git-fetch use CR
to skip back to the start of the current line and redraw it with
an updated progress.  We were doing this in our Tk widget but had
failed to skip the CR, which Tk doesn't draw well.

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