- optionally returns centre point as well

This reverts commit c5bea524.

This reverts commit b18f6cc1.

STYLE: move inline functions into boundBoxI.H

STYLE: reduce duplicate methods in treeBoundBox

- If the underlying type is contiguous, FixedList hashes its storage directly.
- Drop labelPairHash (non-commutative) from fvMeshDistribute since
  FixedList::Hash does the right thing anyhow.
- Hash<edge> specialization is commutative, without multiplication.
- Hash<triFace> specialization kept multiplication (but now uLabel).
  There's not much point optimizing it, since it's not used much anyhow.

Misc. changes

- added StaticAssert to NamedEnum.H
- label.H / uLabel.H : define FOAM_LABEL_MAX, FOAM_ULABEL_MAX with the
  values finally used for the storage.  These can be useful for pre-processor
  checks elsewhere (although I stopped needing them in the meantime).

- Hash returns unsigned
- FixedList templated on unsigned int
- include uLabel.H in UList, HashTable etc. so the output function is know
  throughout

- make table power-of-two, but since it seems to give 1-2% performance
  improvement, maybe forget it too.

- remove two-argument form of hashing classes and do the modulus direclty
  within HashTable instead. This simplifies things a fair bit.

- migrate Hash<void*> from db/dlLibrary to primitives/hashes/Hash

- plain nTriangles() inline method for face class
  - triFace gets the same for symmetry
  - face::triangles(), face::trianglesQuads() return the number of faces generated
  - face::triangles() can append to a DynamicList

because I failed to work out how to merge Mark's stuff -- HELP!!!

Added edgeDirection methods for face/triFace.
Added extra constructors for converting faces to triFaces.
The collapse() method now returns the new face size and can be used to check
if the collapse face is valid.