Bug fix for OS_WIN32: Replaced errno with WSAGetLastError() where result is compared with WSAE... codes.

Per http://msdn.microsoft.com/en-us/library/windows/desktop/ms737828%28v=vs.85%29.aspx
Error codes set by Windows Sockets are not made available through the
errno variable.

Comparison of errno values with WSAE codes was causing EventMachine
to spontaneously close socket connections when the errno value didn't
match the expected WSAE codes.