Initial commit of cliptest work. More to come shortly.

Initial commit of cliptest work.  More to come shortly.

 - Add debug, benchmark code.
 - Change linux/x86 FAST_MATH code to GCC/x86, and clear FP exceptions
   before exiting the fast math block.
 - Remove divide-by-zero test in x86 cliptest, and set clipped vertices
   to [0,0,0,1] instead of leaving them uninitialized.