Don't call dnn_version if user disable dnn!

theano/sandbox/cuda/__init__.py

@@ -576,6 +576,7 @@ def use(device,
                 cudnn_version = "not available"
                 warn = None
                 try:
+                    if dnn_available():
                         (hdr_v, runtime_v) = dnn_version()
                         cudnn_version = runtime_v
                         # 4100 should not print warning with cudnn 4 final.