Use SetSystemPaletteUse() to get better access to the system palette.

We can still do better palette matching in the case where we aren't
using fullscreen mode or a hardware palette, but that can wait for
another day. :)

--HG--
branch : SDL-1.2
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/branches/SDL-1.2%402398