Cycles: enable multi closure sampling and transparent shadows only on CPU and

CUDA cards with shader model >= 2 for now (GTX 4xx, 5xx, ..). The CUDA compiler
can't handle the increased kernel size currently.

intern/cycles/device/device_cuda.cpp

@@ -181,6 +181,14 @@ public:
 		cuda_assert(cuCtxDetach(cuContext))
 	}
 
+	bool support_full_kernel()
+	{
+		int major, minor;
+		cuDeviceComputeCapability(&major, &minor, cuDevId);
+
+		return (major >= 2);
+	}
+
 	string description()
 	{
 		/* print device information */