Fix Win32/Cygwin problems:

After updating to the latest cvs, and also building most of the addons
(like PLs), the following patch is neededf for win32 + Visual C++.

* Switch to use the new win32 semaphore code
* Rename win32_open to pgwin32_open. win32_open collides with symbols
defined in Perl. MingW didn't detect ig, MSVC did. And it's a bit too
generic a name to export globally, imho...
* Python defines some partially broken #pragmas in the headers when
doing a debug build. Workaround.

Magnus Hagander