This change reverts the RTree API back to the original one (i.e.
insert() instead of put(), search() instead of find()), and
creates a new searchReturningObject() method that returns an
object keyed by UIDs.
It also adds missing tests for type restricted search and
searchReturningObject().
This new implementation is based on
http://github.com/imbcmdth/RTree/, with only a few modifications
to add the optional type and provide the API of the previous
implementation.
There is still room for optimization, but this is such an
improvement over the previous RTree already that it's worth
bringing it in now.
