- made vtkScalarsToColors::SetRange(double[2]) virtual, since the other SetRange() is.  Likewise vtkLookupTable::SetTableRange(double[2]).
- changed most uses of dangerous GetTableValue() (that returns inner buffer) in favour of version that copies the values out.
- use fixed-size memcpy in a few places for a potential speedup
- improved some comments
- added a few consts, especially with buffers
- removed const on plain old ints
- moved a nan check earlier, saving work when true
- moved some variable declarations closer to initialization
- removed some unneeded semi colons
- removed some useless casts, added others for clarity