Patch by Mark Hammond:

* Changes to a recent patch by Chris Tismer to errors.c.  Chris' patch
always used FormatMessage() to get the error message passing the error code
from errno - but errno and FormatMessage use a different numbering scheme.
The main reason the patch looked OK was that ENOFILE==ERROR_FILE_NOT_FOUND -
but that is about the only shared error code :-).  The MS CRT docs tell you
to use _sys_errlist()/_sys_nerr.  My patch does also this, and adds a very
similar function specifically for win32 error codes.