needed now that fcntl exports the constants.

based on the termios module.  The only added "feature" is the deprecation
warning it spits out.

the standard library does not use the SOCKET module any more, and it is
not defined for all platforms (Windows, in particular).

Use != instead of <> since <> is documented as "obsolescent".
Use "is" and "is not" when comparing with None or type objects.

genuine bug, so I checked it in separately.

Don't use CL module since all constants are now in cl.