pull: use $curr_branch_short more
pull: use $curr_branch_short more

One of the first things git-pull.sh does is setting $curr_branch to
the target of HEAD and $curr_branch_short to the same but with the
leading "refs/heads/" removed.  Simplify the code by using
$curr_branch_short instead of setting $curr_branch to the same
shortened value.

The only other use of $curr_branch in that function doesn't have to
be replaced with $curr_branch_short because it just checks if the
string is empty.  That property is the same with or without the prefix
unless HEAD points to "refs/heads/" alone, which is invalid.

Noticed-by: Felipe Contreras <de77a8b9cd239b204c19c52ed62e48ab47243362@gmail.com>
Signed-off-by: Rene Scharfe <2da278a99b557fc93ddbed7517a413ad793e2e6a@web.de>
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