Adding a _frame argument to InterfaceClass.__init__ to make it subclassable

Hi,

I'd like to apply the attached patch to zope.interface trunk to make
it more easily subclassable without having to copy and paste a chunk
of its __init__ into the subclass' __init__.

Motivating factor is: I need an Interface with a hook that gets called
after InterfaceClass.__init__ to allow for:

* Checking that field names supplied as tagged values from directives
correspond to actual field names to detect typos.
* Registering the Interface instance for further configuration to be
executed by a zope.configuration action.

(Subclass is http://dev.plone.org/plone/browser/plone.supermodel/branches/elro-directives/plone/supermodel/model.py#L52)

Laurence

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Index: src/zope/interface/interface.py
===================================================================
--- src/zope/interface/interface.py	(revision 121491)
+++ src/zope/interface/interface.py	(working copy)
@@ -434,7 +434,7 @@
     #implements(IInterface)
 
     def __init__(self, name, bases=(), attrs=None, __doc__=None,
-                 __module__=None):
+                 __module__=None, _frame=1):
 
         if attrs is None:
             attrs = {}
@@ -448,7 +448,7 @@
                     # Figure out what module defined the interface.
                     # This is how cPython figures out the module of
                     # a class, but of course it does it in C. :-/
-                    __module__ = sys._getframe(1).f_globals['__name__']
+                    __module__ = sys._getframe(_frame).f_globals['__name__']
                 except (AttributeError, KeyError):
                     pass