socket.py is used for all platforms, and it defines the additional
classes and alternate socket() function for Windows and BeOS systems.

The plat-*/socket.py files are no longer needed, since there is a
shared socket.py.

make_fqdn() is provided, but I decided to call it getfqdn() to be
consistent with the other names in the socket module.  Since it is
really a "get" operation and does not create a new name, this is
the right name to give it.

Move the docstring here from the _socket module.