Passing a string into zope.interface.implements causes infinite recursion

[tseaver]

In https://bugs.launchpad.net/zope.interface/+bug/113672, @faassen reported

We know you're not supposed to pass a stirng into zope.interface.implements, but try the following:

>>> from zope.interface import implements
>>> class Foo(object):
... implements('foo')

the prompt will hang for a while. Then we get this error:

File "/home/faassen/buildout/grok-eggs/eggs/tmpxXgh8b/zope.interface-3.4.0a1-py2.4-linux-i686.egg/zope/interface/declarations.py", line 1370, in _normalizeargs
File "/home/faassen/buildout/grok-eggs/eggs/tmpxXgh8b/zope.interface-3.4.0a1-py2.4-linux-i686.egg/zope/interface/declarations.py", line 1370, in _normalizeargs
File "/home/faassen/buildout/grok-eggs/eggs/tmpxXgh8b/zope.interface-3.4.0a1-py2.4-linux-i686.egg/zope/interface/declarations.py", line 1366, in _normalizeargs
RuntimeError: maximum recursion depth exceeded in cmp

Perhaps something can be done to prevent this infinite recursion. Not urgent, but would be nice as this is rather surprising.

[tseaver]

Note that the more modern @implementer idiom fails similarly.

[jamadden]

The variety of things that _normalizeargs accepts makes this a complicated problem, especially since it's involved at import time and we don't want to slow that down. Perhaps a simple assert not isinstance(sequence, str) handles this well enough?