GSocket has a timeout flag now, but when using GSocketClient there was
no way to set the timeout until after connecting (or failing). Fix
that by adding a timeout property to GSocketClient.
The whole protocol name thing is pretty weird. The getprotobyname functions
seem to only specify one mapping for name <-> ids, so all families/types
must use the same values. Plus the values used for the protocols are
standardized by IANA, so are always the same.
So, we drop using names for protocols, intead introducing an enum with
a few commonly availible and used protocols.
