[PD-dev] [GEM] more cvs commits

[chris clepper]

the following commits only affect the OSX version of GEM:

added altivec to some of the yuv objects:
- yuv_add
- yuv_adjust
- yuv_gain
- yuv_mix
- yuv_subtract

added a cache calculation function to GemPixObj.h

to compile with altivec use gcc -faltivec -DALTIVEC

speed improvements range from 400 to 725%

the next step is adding some sort of processImageYUVAltivec to the 
related pix_objects...

cgc