make tester produce useful help messages

Also, try to set the HAVE_NEWBUFFER flag more accurately

Add file.isatty
sys.exit(None) -> exit code 0
non-dict kwargs
hash(function)
CPython's implementation of PyCallIter

add a json test and get it running

Bunch of small missing features, but with these and some small
workarounds inside django, we can run django-admin to the point
that it gives us the help message and then quits.

This is needed for defaultdict

Also make some of the functions work correctly with list subclasses.

We used to just ignore these, but we can call these from
the proxy_to_tp_traverse and proxy_to_tp_clear adapters.

We already did proper index handling in setitem but hadn't ported
it to delitem; now delitem just delegates to setitem.

Also add instance.__contains__

The organization is kind of hacky since we have to copy str_rsplit
into stringobject.c so it can be use stringlib, but we want to reference
it from str.cpp.

there are a few areas where we fail (decimal usage, and formatting complex numbers)
so those specific lines are commented out.

The changes in src were necessary to get the test to run to completion with -n.
Finally, we skip the test when -x is present because pypa doesn't parse unicode
literals correctly.

add support for relative imports, and bring our import api closer to cpython

copy _PyInt_Format implementation from cpython

add an explanatory comment about why we set level = -1 if we're missing `from __future__ import absolute_import`

Add the io/_io Module and make import gzip work

Treat unicode names as equivalent to their ascii-encoded str
version, and any non-ascii unicode name as a TypeError.

My hope is that this covers the common cases but doesn't cause
bugs.  You can see that we're doing this by putting unicode in
and getting a str out, but I hope that this is ok.

This adds quite a few C API functions
and I had to introduce atleast two temporary hacks:
- do not depend on the ABC module which uses weak references
- use a dummy PyErr_CheckSignals() function