Grind IndexedPaletteBackground for performance

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Suggestions:
* Get rid of modulo:
  - Use LUT?
  - http://embeddedgurus.com/stack-overflow/2011/02/efficient-c-tip-13-use-the-modulus-operator-with-caution/
* Look for opportunities to use bit operations
* Look into using "fast" datatypes from cstdint: 
http://embeddedgurus.com/stack-overflow/2008/06/efficient-c-tips-1-choosing-the-
correct-integer-size/
* Use memcpy where appropriate.

Original issue reported on code.google.com by jeff.bac...@gmail.com on 28 Nov 2013 at 1:31