* Added add, subtract, multiply operators to Color4
* Switched baking to use Color4 instead of System.Drawing.Color
* Untested implementation of multiply and add color operations in baking
git-svn-id: http://libopenmetaverse.googlecode.com/svn/libopenmetaverse/trunk@3077 52acb1d6-8a22-11de-b505-999d5b087335