The extended PALETTE.DAT format can now carry a trailing byte, called
'lognumalphatables'. If it is present, the engine assumes that alpha blending
tables are loaded at blend indices 1 to 1<<lognumalphatables and handles
rotatesprite's alpha and spriteext[].alpha accordingly.
The ability to save this new byte is added to engine.lua:savePaletteDat()
and the corresponding convenience functions in shadexfog.lua.
Examples test/screentext.con and test/sprite_access.con are updated for
demonstration purposes.
git-svn-id: https://svn.eduke32.com/eduke32@4426 1a8010ca-5511-0410-912e-c29ae57300e0
