Rewrite unaryop and property get

more capi exceptions

I think we track the dependency correctly in cmake, but distutils
doesn't know that the system headers can change from underneath it,
so manually specify them as extra dependencies.

Previously, if a CAPI-style callsite tried to call a function but
only CXX versions were available (and visa versa), it would bail
on rewriting.  Now enable CAPI rewrites of CXX functions by using
a helper function, and enable CXX rewrites of CAPI functions by
just calling checkAndThrowCAPIException like we normally do.

note: people need to `find -name '*.pyston.so' -delete`, since although
I think we correctly know to try to rebuild the sharedmodules,
distutils won't end up rebuilding it.

and friends.  Should be pretty much the last step for letting
calls go all the way through our runtime using CAPI exceptions.

add __doc__ attribute to capifunc

Refactor location and names of gc visit functions.

This serves two purposes.
1) Improve naming consistency (follow the format TYPENAME::gcHandler)
2) In the source file, the visit function declaration is closer to the
   fields of the objects. If a field is added, hopefully it will be
   easier to remember to update the GC visit function.

Add "doctest" support

My guess is that there's a build dependency issue, where
we try building files that include libunwind.h before we
run the rules that generate it.  Not sure why we weren't running
into that before.  But the normal c++ files in src/ correctly
depend on libunwind, but the ones in src/runtime/inline don't
seem to.

For good measure, don't include libunwind.h in our header files,
and just use forward-declaring.

ie what you create either on the repl (where we were close) or
with `exec compile(foo, bar, "single")` (where we were not so close).

With these changes, doctest seems to mostly be working.

This was stemming from our use of the HEAPTYPE flag for our builtins,
and cpython inferring "is builtin" from that.

Also, fix a couple other minor things that I ran into.

object.__str__ use capi slot in order to increase compatibility with cpython

With this change we print True for:
class C(object):
    pass
print C.__str__ is object.__str__

Cheetah depends on this behaviour (see https://bitbucket.org/pypy/compatibility/wiki/cheetah)

Move our integration tests to a separate repository

By default it just does `git submodule init`