Escape --upload-pack from expr.

Escape --upload-pack from expr.

Recent commit ae1dffcb28ee89a23f8d2747be65e17c8eab1690 by Junio
changed the way --upload-pack was passed around between clone,
fetch and ls-remote and modified the handling of the command
line parameter parsing.

Unfortunately FreeBSD 6.1 insists that the expression

  expr --upload-pack=git-upload-pack : '-[^=]*=\(.*\)'

is illegal, as the --upload-pack option is not supported by their
implementation of expr.

Elsewhere in Git we use z as a leading prefix of both arguments,
ensuring the -- isn't seen by expr.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>