create an is_callable method for all representation objects, to determine if something is callable or not

jedi/parser/representation.py

@@ -118,6 +118,13 @@ class Base(object):
             scope = scope.parent
         return scope
 
+    def is_callable(self):
+        """
+        By default parser objects are not callable, we make them callable by
+        the ``evaluate.representation`` objects.
+        """
+        return False
+
     def space(self, from_pos, to_pos):
         """Return the space between two tokens"""
         linecount = to_pos[0] - from_pos[0]