[PATCH 0/2] Avoid spending cycles to deltify binary guck

Somebody wondered on #git if there is a way to avoid spending
cycles and memory on certain objects in a repository, most
notably huge image files (or it might have been porn video
collection, but I do not recall the details).

Here is a quick-and-clean patch series to help such a repository.

 [PATCH 1/2] pack-objects: pass fullname down to add_object_entry()
 [PATCH 2/2] Teach "delta" attribute to pack-objects.

Although we give pack-objects the pathname for each blob, we
used to hash it down before registering the object to
object_entry array.  The first one moves the call site to the
hash function a bit, to give add_object_entry() to inspect the
pathname.

The second patch teaches add_object_entry() to record if an
entry should be exempt from the deltification process, and use
the .gitattributes mechanism to tell which objects should be
marked as such.

The patches are based on np/pack series, and should apply
cleanly to 'next'.