Add test for mixing STL casters and local binders across modules

[dean0x7d]

This is an attempt to address one of the lingering questions from #919. Even if it doesn't directly answer that, it's still a useful test to add.

One module uses a generic vector caster from <pybind11/stl.h> while the other exports std::vector<int> with a local py:bind_vector. The vector caster from <pybind11/stl.h> accepts anything that looks like a sequence, so it will happily load the py::module_local opaque vector from a different module. Even if it can't see it's C++ type data, it still behaves like a sequence and can be converted generically.

Note: Type aliases and PYBIND11_MAKE_OPAQUE needed to be added for several types because of the inclusion of <pybind11/stl.h>.

[jagerman]

Nice! I didn't actually realize that would work, but it's nifty that it does.