git clean: Don't automatically remove directories when run within subdirectory

git clean: Don't automatically remove directories when run within subdirectory

When git clean is run from a subdirectory it should follow the normal
policy and only remove directories if they are passed in as a pathspec,
or -d is specified.

The fix is to send len which could be shorter than ent->len because we
have stripped the trailing '/' that read_directory adds. Additionaly
match_one() was modified to allow a name[] that is not NUL terminated.
This allows us to check if the name matched the pathspec exactly
instead of recursively.

Signed-off-by: Shawn Bohrer <shawn.bohrer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>