Cycles: OpenCL image texture support, fix an attribute node issue and refactor

feature enabling #defines a bit.

intern/cycles/device/device_cuda.cpp

@@ -877,6 +877,7 @@ void device_cuda_info(vector<DeviceInfo>& devices)
 		int major, minor;
 		cuDeviceComputeCapability(&major, &minor, num);
 		info.advanced_shading = (major >= 2);
+		info.pack_images = false;
 
 		/* if device has a kernel timeout, assume it is used for display */
 		if(cuDeviceGetAttribute(&attr, CU_DEVICE_ATTRIBUTE_KERNEL_EXEC_TIMEOUT, num) == CUDA_SUCCESS && attr == 1) {