Merge Maurits's r89745 as well: Proper English spelling of "cannot".

PythonScript.py

@@ -325,7 +325,7 @@ def _exec(self, bound_names, args, kw):
         try:
             result = f(*args, **kw)
         except SystemExit:
-            raise ValueError('SystemExit can not be raised within a PythonScript')
+            raise ValueError('SystemExit cannot be raised within a PythonScript')
 
         if keyset is not None:
             # Store the result in the cache.