Cmake add pwdmodule, slots_test, and match existing test configurations

fixes #238 CMake issues

We weren't able to exit if we had a thread running in the background,
since we released the GIL at the end of the C level main() and the
background thread would start running again after all the data structures
had been torn down.

Now, just keep holding the GIL as we exit.

Was tired of seeing bare "unimplemented" error messages and having
to track down where they were coming from -- especially tricky
when trying to add fork() support and the errors were in the child.

- int(bool) works
- hash(bool) works
- str.find() now takes an optional "start" parameter

- Set the import "level" appropriately (takes absolute_import flag into account)
- Add a basic implementation of the __import__() function
- Fix a bug in existing import behavior (would not check sys.modules in certain
  cases)

ie running setup.py under Pyston.

Doesn't work yet, but (in a separate branch) was able to hack up
the distutils library until it did!

-these should now be skipped for python < 2.7.4, not >= 2.7.4
-check-pyston now passes on ubuntu 12.04 (including travis-ci.org) and 14.04

-now we only build the parts of llvm that are actually required

I thought we weren't going to be able to do it since posixmodule.c
is 9kloc, but it's working!

Had to make one modification to posixmodule.c where it was directly
accessing the fd of a file object; haven't figured out the best way
to handle this.

Should probably reorganize/rename the "lib_python" directory at some point.

Somehow had gotten the C API definitions of True and False backwards...

This is so that we can add the CAPI slots for things like tp_as_sequence,
so that C extensions will work properly.

I don't think there are very many extensions that would do this but let's
still support it for now; it further bloats the type objects but only as
much as it does in CPython as well.

Previously had hardcoded three different iterations.