- added boundBox(const tmp<pointField>&) constructor for use with
coordinate systems
- moved some methods from treeBoundBox to boundBox and use VectorSpace ops
- operator+= : add in the listed keys
- operator-= : remove the listed keys
- operator&= : intersection of keys
- added xfer constructor (just in case)
- moved labelHashSet typedef to HashSet.H, for consistency with the
wordHashSet typedef being there and since it is used so often