Fix genshi.core.Attrs.__contains__ so that it returns False instead of None if an attribute is not found (CPython translates this to False automatically but PyPy does not).
Fix genshi.core.Attrs.__contains__ so that it returns False instead of None if an attribute is not found (CPython translates this to False automatically but PyPy does not).

mitchellrj/genshi,mitchellrj/genshi,mitchellrj/genshi,mitchellrj/genshi