HAMMER Utilities: Use a Red-Black tree to track HAMMER TIDs, use diff -N

HAMMER Utilities: Use a Red-Black tree to track HAMMER TIDs, use diff -N

Begin using a red-black tree to track the TIDs used to generate diff sets.

Use diff -N to deal with pre-creation/post-creation undo diffs.

Use diff -r.  However, running undo -a -d on a directory is not yet
meaningful because only the directory TIDs are used right now.