Continued progress with reintroducing testing on the new metadata logging

Now with some tweaks to commit/compact, and a committers for entrylists and
moves specifically. No longer relying on a commitwith callback, the
types of commits are now infered from their tags.

This means we can now commit things atomically with special commits,
such as moves. Now lfs_rename can move entries to new names correctly.

tests/test_dirs.sh

@@ -329,7 +329,7 @@ tests/test.py << TEST
 TEST
 
 echo "--- Multi-block remove ---"
-tests/test.py << TEST
+tests/test.py -s << TEST
     lfs_mount(&lfs, &cfg) => 0;
     lfs_remove(&lfs, "cactus") => LFS_ERR_NOTEMPTY;