filter-branch: make sure orig_namespace ends with a single slash.
filter-branch: make sure orig_namespace ends with a single slash.

Later in a loop any existing ref whose path begins with it is
removed.  It would be a disaster if you allowed it to say refs/head
for example.

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