prompt: fix untracked files for zsh
prompt: fix untracked files for zsh

We signal presense of untracked files by adding a per-cent sign '%'
to the prompt.  But because '%' is used as an escape character to
introduce prompt customization in zsh (just like bash prompt uses
'\' to escape '\u', '\h', etc.), we need to say '%%' to get a
literal per-cent.

Helped-by: Andreas Schwab <c9df6394cb541f693236245820fbe23866f1a3fe@linux-m68k.org>
Signed-off-by: Felipe Contreras <de77a8b9cd239b204c19c52ed62e48ab47243362@gmail.com>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git