I really needed the well-wishing with regard to buffer sizing :-)

Here's a patch for a couple of fronts:
- Teach os.unlink about junction points
- Introduce _winapi.CreateJunction
- Introduce a new test suite in test_os.py for junction points

I pulled the definition of _REPARSE_DATA_BUFFER out into a new header called winreparse.h.

I'd appreciate critical review of _winapi.CreateJunction to make sure I haven't missed anything. I'm not familiar with the Python/C interop idioms, so I might have missed something wrt arguments/return values handling.

Happy new year!