Make @implementer and classImplements not add redundant interfaces

[jamadden]

The plone buildout.coredev tests all pass, with the exception of 8 tests from plone.app.caching.tests.test_etags. They all fail like this:

Error in test test_Roles_member (plone.app.caching.tests.test_etags.TestETags)
Traceback (most recent call last):
  File "//2.7/lib/python2.7/unittest/case.py", line 329, in run
    testMethod()
  File "//plone.app.caching-2.0.4-py2.7.egg/plone/app/caching/tests/test_etags.py", line 144, in test_Roles_member
    provideAdapter(DummyPortalState, name=u'plone_portal_state')
  File "//zope.component-4.5-py2.7.egg/zope/component/globalregistry.py", line 73, in provideAdapter
    base.registerAdapter(factory, adapts, provides, name, event=False)
  File "//src/zope.interface/src/zope/interface/registry.py", line 305, in registerAdapter
    provided = _getAdapterProvided(factory)
  File "//src/zope.interface/src/zope/interface/registry.py", line 528, in _getAdapterProvided
    "The adapter factory doesn't implement a single interface "
TypeError: The adapter factory doesn't implement a single interface and no provided interface was specified.

That's with code like this:

       @implementer(Interface)
       @adapter(DummyContext, Interface)
        class DummyPortalState(object):

            def __init__(self, context, request):
                pass

            def language(self):
                return 'en'

        provideAdapter(DummyPortalState, name=u'plone_portal_state')

Something is going wrong with @implementer(Interface)...

[jamadden]

Latest commits make plone's buildout.coredev green for me. Currently based on #202.

[jamadden]

Rebased on master.

[mgedmin]

LGTM

[mgedmin]

Does pylint not complain about using lowercase-ell as a variable name?

[jamadden]

It probably would, but the check for valid names has to be disabled when working in zope repos because the false positives are overwhelming. (It's not the first one-letter temporary variable in this file.)

[jamadden]

Thank you.