GPU optimization and code clean[revised]

Cleaned up a lot of the GPU pwsafe code and applied more optimizations.  Also fixed the clobbering issue with the multiple GPUs and tweaked some opencl values when testing.

Here are the benchmarks.
Device 1: Tahiti (AMD Radeon HD 7900 Series)
Local worksize (LWS) 64, Global worksize (GWS) 262144
Benchmarking: Password Safe SHA-256 [OpenCL]... DONE
Raw:	494611 c/s real, 78643K c/s virtual

Benchmarking: Password Safe SHA-256 [CUDA]... DONE
Raw:	128862 c/s real, 128862 c/s virtual