safe_create_leading_directories(): add explicit "slash" pointer
safe_create_leading_directories(): add explicit "slash" pointer

Keep track of the position of the slash character independently of
"pos", thereby making the purpose of each variable clearer and
working towards other upcoming changes.

Signed-off-by: Michael Haggerty <c24c152f145c57791e809b126db9e61bd1c1782d@alum.mit.edu>
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