commit-reach: fix memory and flag leaks

commit-reach: fix memory and flag leaks

The can_all_from_reach_with_flag() method uses 'assign_flag' as a
value we can use to mark objects temporarily during our commit walk.
The intent is that these flags are removed from all objects before
returning. However, this is not the case.

The 'from' array could also contain objects that are not commits, and
we mark those objects with 'assign_flag'. Add a loop to the 'cleanup'
section that removes these markers.

Also, we forgot to free() the memory for 'list', so add that to the
'cleanup' section.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>