propose to rename natPlainSocketImpl to natPosixPlainSocketImpl

[Tom Tromey]

>>>>> "Nic" == Nic Ferrier <nferrier@tapsellferrier.co.uk> writes:

Nic> Personally, I think it would be better if there was a separation,
Nic> although that might mean that once we have a Windows port it lags
Nic> behind any changes to the posix stuff.

Once it is fully functional, we could require that changes not break
the Windows port.

Tom