FIX: don't expose internals to outside world

Was returning refs to dicts stored in _left at bottom of the stack.
This means any mutation to these objects gets reflected back down into
the cycler with out any of the keys being updated etc.

Author: tacaswell

cycler.py

@@ -129,7 +129,7 @@ def __getitem__(self, key):
 
     def __iter__(self):
         if self._right is None:
-            return iter(self._left)
+            return iter(dict(l) for l in self._left)
 
         return self._compose()