(svn r2702) -Codechange: Cleaned up the sprite code and replaced many magic numbers

by enums. There remains work in gfx.c to move the "transparency" and
"recolor" bits around to make space for more sprites. However, 2800
additional sprites can now be loaded. There also remains cleanup and
Doxygen work on many of the header files.

gfx.h

@@ -104,11 +104,6 @@ VARDEF int _pal_last_dirty;
 
 VARDEF bool _use_dos_palette;
 
-/* spritecache.c */
-//enum { NUM_SPRITES = 0x1320 };
-//enum { NUM_SPRITES = 0x1500 };
-enum { NUM_SPRITES = 0x3500 }; // 1500 + space for custom GRF sets
-
 typedef struct Colour {
 	byte r;
 	byte g;