to avoid problems loading the CRT from a private assembly.  Via bug 4566.

The "can't load dll" message box on Windows is suppressed while an extension is loaded by calling SetErrorMode in dynload_win.c. The error is still reported properly.

On Windows, when import fails to load a dll module, the message says
"error code 193" instead of a more informative text.

It turns out that FormatMessage needs additional parameters for some error codes.
For example: 193 means "%1 is not a valid Win32 application".
Since it is impossible to know which parameter to pass, we use
FORMAT_MESSAGE_IGNORE_INSERTS to get the raw message, which is still better
than the number.

- update header checks, using autoconf
- provide dummies for getenv, environ, and GetVersion
- adjust MSC_VER check in socketmodule.c

table' of the dll, to make sure that the dll really was build for the
correct Python version.  It does this by looking for an entry
'pythonXY.dll' (X.Y is the Python version number).

The code now checks the size of the dll's import table before reading
entries from it.  Before this patch, the code crashed trying to read
the import table when the size was zero (as in Win2k's wmi.dll, for
example).

Look for imports of 'pythonXY_d.dll' in a debug build instead of
'pythonXY.dll'.

Fixes SF 951851: Crash when reading "import table" of certain windows dlls.

Already backported to the 2.3 branch.