Changes to PC\config.[hc] for Win64. MSVC defines _WINxx to differentiate the
various windows platforms. Python's MS_WINxx are keyed off of these. Note
that _WIN32 (and hence MS_WIN32 in Python) are defined on Win32 *and* on
Win64. This is for compatibility reasons. The idea is that the common case is
that code specific to Win32 will also work on Win64 rather than being
specific to Win32 (i.e. there is more the same than different in WIn32 and
Win64).

The following modules are specifically excluded in the Win64 build:
audioop, binascii, imageop, rgbimg. They are advertised as heavily 32-bit
dependent.  [They should probably be fixed!  --GvR]

The patch to config.h looks big but it really is not. These are the effective
changes:
- MS_WINxx are keyed off _WINxx
- SIZEOF_VOID_P is set to 8 for Win64
- COMPILER string is changed appropriately for Win64