Fix-up previous expr changes.

Fix-up previous expr changes.

The regexp on the right hand side of expr : operator somehow was
broken.

	expr 'z+pu:refs/tags/ko-pu' : 'z\+\(.*\)'

does not strip '+'; write 'z+\(.*\)' instead.

We probably should switch to shell based substring post 1.3.0;
that's not bashism but just POSIX anyway.

Signed-off-by: Junio C Hamano <junkio@cox.net>