Classifier demo: Check the mode before checking classifierModel.

For #65.

demos/classifier.py

@@ -145,9 +145,10 @@ if __name__ == '__main__':
 
     args = parser.parse_args()
 
-    if args.classifierModel.endswith(".t7"):
+    if args.mode == 'infer' and args.classifierModel.endswith(".t7"):
         raise Exception("""
-Torch network model passed as the classification model.
+Torch network model passed as the classification model,
+which should be a Python pickle (.pkl)
 
 See the documentation for the distinction between the Torch
 network and classification models: