repo: Require lock type in ostree_repo_lock_pop

This simplifies the lock state management considerably since the
previously pushed type doesn't need to be tracked. Instead, 2 counters
are kept to track how many times each lock type has been pushed. When
the number of exclusive locks drops to 0, the lock transitions back to
shared.

tests/test-core.js

@@ -137,9 +137,9 @@ assertEquals(actual_checksum, networks_checksum)
 // Basic locking API sanity test
 repo.lock_push(OSTree.RepoLockType.SHARED, null);
 repo.lock_push(OSTree.RepoLockType.SHARED, null);
-repo.lock_pop(null);
-repo.lock_pop(null);
+repo.lock_pop(OSTree.RepoLockType.SHARED, null);
+repo.lock_pop(OSTree.RepoLockType.SHARED, null);
 repo.lock_push(OSTree.RepoLockType.EXCLUSIVE, null);
-repo.lock_pop(null);
+repo.lock_pop(OSTree.RepoLockType.EXCLUSIVE, null);
 
 print("ok test-core");