defer.py: Remove py3k deprecation warnngs when running twistedl/test

New submission from drtimcouper <None>:

To demonstrate success:

1. Run trial twisted/test and save the deprecation warnings in a file (so that's 2>1)
2. Apply the patch
3. Run trial twisted/test again to another file, and diff the two.
There should be no defer.py references in the second file which refer to py3k deprecations

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Type     : enhancement
Component: core
Keywords : 
Priority : normal
Nosy     : 
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http://twistedmatrix.com/trac/ticket/4301