Color: Moved SColor* structs into SColor.h, so they can be used without
indirectly including CVector[34]D.
Terrain: Added 'base colour', for the Actor Viewer to be able to
modulate the colour of normally-white terrain.
Removed some "using namespace std" (because it doesn't make the code
easier to read, and it defeats the point of namespaces, and the rest of
the code doesn't do it).
This was SVN commit r4392.
