Removed duplicate pack loading code

The "GET" command and "ca-cas-repack --full" now share code paths for loading
pack files.

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>
Add more fuzz to end-to-end test

Insert 27 more objects, test for existence, repack, then test for existence
again.

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>
Add ca-cas-prune-packed

This command removes loose objects that exist in pack files.

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>