git-svn gc: trigger incremental packing if "lotsa" single-object packs

git-svn gc: trigger incremental packing if "lotsa" single-object packs

Add new `lotsa_loose_objects_or_sopacks` function and call it instead
of `lotsa_loose_pruned_objects` when deciding whether or not to call
`pack_incremental_loose_objects_if_lockable`.

When `git-svn fetch` spits out a whole bunch of single-object packs,
they will now be combined at the next opportunity even when there
are no actual loose objects (or not enough to trigger a packing).

Force `gc.autoPackLimit=1` during any `git-svn` clone/update operation
to make sure that an opportunity arises to combine single-object
packs even when there are no loose objects themselves.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>