[AD] New poly3d routine

I'm not sure if anyone is interested in, but here is a new poly3d.c file : I have completly rewritten it in order to :

1. Get speed enhancements

2. Add triangle3d() functions which take constant gradients into account (gradients are calculated once at the beginning of the routine)

3. Add subpixel and subtexel accuracy

If you want to put it in the Allegro library just replace the old 'poly3d.c' file by the attached one and then recompile the library. That's all !!! I have taken 'Const'-correctness into account.

At the very beginning of the file, there is a function called fceil() which is a fixed point version of ceil(). I wrote a C version and a ASM 386 version in GCC format (sorry for MSVC and Watcom owners : I couldn't write a version for those compilers since I don't know their asm format). If you think anyone can use fceil() in any way, it can be moved in alinline.h and al386gcc.h (and also in al386vc.h and al386wat.h provided that someone write the corresponding versions).

Bertrand.