rev-list: add an option to mark fewer edges as uninteresting

In commit fbd4a70 (list-objects: mark more commits as edges in
mark_edges_uninteresting - 2013-08-16), we marked an increasing number
of edges uninteresting.  This change, and the subsequent change to make
this conditional on --objects-edge, are used by --thin to make much
smaller packs for shallow clones.

Unfortunately, they cause a significant performance regression when
pushing non-shallow clones with lots of refs (23.322 seconds vs.
4.785 seconds with 22400 refs).  Add an option to git rev-list,
--objects-edge-aggressive, that preserves this more aggressive behavior,
while leaving --objects-edge to provide more performant behavior.
Preserve the current behavior for the moment by using the aggressive
option.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
pack-objects: use --objects-edge-aggressive for shallow repos

When fetching into or pushing from a shallow repository, we want to
aggressively mark edges as uninteresting, since this decreases the pack
size.  However, aggressively marking edges can negatively affect
performance on large non-shallow repositories with lots of refs.

Teach pack-objects a --shallow option to indicate that we're pushing
from or fetching into a shallow repository.  Use
--objects-edge-aggressive only for shallow repositories and otherwise
use --objects-edge, which performs better in the general case.  Update
the callers to pass the --shallow option when they are dealing with a
shallow repository.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>