Re-enable pbc_merge tests, since it's a real problem that needs fixing rather than a bad test. Also add an extra test.
Re-enable pbc_merge tests, since it's a real problem that needs fixing rather than a bad test. Also add an extra test.

git-svn-id: 6e74a02f85675cec270f5d931b0f6998666294a3@9827 d31e2699-5ff4-0310-a27c-f18f2fbe73fe

ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot