GFXLIB: fix signed/unsigned mismatches.
GFXLIB: fix zero-ing memory shortcut trickery.
GFXLIB: fix uninitialised value warnings.
PICDRIVE: delete buildpdr.h.
PICDRIVE: delete truepdr.h.
PICDRIVE: delete inc/gif.h and flilo/gif.h.
PICDRIVE: sluff pdr_rgb_seekstart and pdr_rgb_readline.