Allow disable of W601

Example library which uses the "has_key" method:

http://apt.alioth.debian.org/python-apt-doc/library/apt.cache.html#apt.cache.Cache.has_key

While has_key no longer exists for python 3, there are still libraries
which have this method and do not allow for 'key in dict'. This enables
the "nopep8/noqa" methods of disabling the warning per-line.

Signed-off-by: Sol Jerome <sol.jerome@gmail.com>