Fixes #21

The 'mostly' is because interfaces are used in cases that C3 forbids;
when there's a conflict, we fallback to the legacy algorithm. It turns
out there are few conflicts (13K out of 149K total orderings in Plone).

I hoped the fix for #8 might shake out automatically, but it didn't.

Optimize the extremely common case of a __bases__ of length one.

In the benchmark, 4/5 of the interfaces and related objects have a base of length one.

Fix the bad IROs in the bundled ABC interfaces, and implement a way to get warnings or errors.

In running plone/buildout.coredev and tracking the RO requests, the
stats for equal, not equal, and inconsistent-so-fallback, I got
{'ros': 148868, 'eq': 138461, 'ne': 10407, 'inconsistent': 12934}

Add the interface module to the Attribute str.

This was extremely helpful tracking down the Plone problem; IDate is defined in multiple modules.

The DEFINE_STRING macro prevents the linter from seeing them as unused
so I temporarily redefined it to find all such variables.

The query functions now start by looking at the next class in the MRO (interfaces directly provided by the underlying object are not found).

Adapter registries automatically pick up providedBy change to start finding the correct implementations of adapters, but to make that really useful they needed to change to unpack super() arguments and pass __self__ to the factory.

Fixes #11

Unfortunately, this makes PyPy unable to build the C extensions.

Additional crash-safety for adapter lookup.

Make the C functions get the cache only after resolving the
``required`` into a tuple, in case of side-effects like...clearing the
cache. This could lead to the ``cache`` object being deallocated
before we used it.

Drop the ``tuplefy`` function in favor of a direct call to
``PySequence_Tuple``. It's what the ``tuple`` constructor would do
anyway and saves a few steps.

Make sure that getting ``providedBy(super())`` and
``implementedBy(super())`` have no side effects.