don't double-decorate in `flag_calls`

IPython/utils/decorators.py

@@ -34,6 +34,10 b' def flag_calls(func):'
     Testing for truth in wrapper.called allows you to determine if a call to
     func() was attempted and succeeded."""
 
+    # don't wrap twice
+    if hasattr(func, 'called'):
+        return func
+
     def wrapper(*args,**kw):
         wrapper.called = False
         out = func(*args,**kw)