Add single color checks to CUDA compressors.

Use optimized bitmap table for CTX compressor.

src/nvtt/cuda/CudaCompressDXT.h

@@ -50,6 +50,7 @@ namespace nv
 	private:
 
 		uint * m_bitmapTable;
+		uint * m_bitmapTableCTX;
 		uint * m_data;
 		uint * m_result;