Make inner_exception optional, and use new except syntax.

rq/exceptions.py

@@ -11,6 +11,6 @@ class NoQueueError(Exception):
 
 
 class UnpickleError(Exception):
-    def __init__(self, message, raw_data, inner_exception):
+    def __init__(self, message, raw_data, inner_exception=None):
         super(UnpickleError, self).__init__(message, inner_exception)
         self.raw_data = raw_data

rq/job.py

@@ -27,7 +27,7 @@ def unpickle(pickled_string):
     """
     try:
         obj = loads(pickled_string)
-    except (StandardError, UnpicklingError), e:
+    except (StandardError, UnpicklingError) as e:
         raise UnpickleError('Could not unpickle.', pickled_string, e)
     return obj