Optimize IDMapper

Simplify code and remove a whole bunch of redundant copies.

Signed-off-by: Adam C. Emerson <aemerson@linuxbox.com>
Clean up uninitialized warning in dbus_message_entrypoint

Signed-off-by: Adam C. Emerson <aemerson@linuxbox.com>
Rewire IDMapper Cache

The last patch didn't touch the cache, just the stuff that queried it.
This patch switches it around to use AVL trees.

Signed-off-by: Adam C. Emerson <aemerson@linuxbox.com>