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_cpu.cpp

@@ -69,6 +69,11 @@ public:
 		kernel_globals_free(kg);
 	}
 
+	bool support_full_kernel()
+	{
+		return true;
+	}
+
 	string description()
 	{
 		return system_cpu_brand_string();