This replaces two previous boolean fields 'resolved' and 'namedpipe',
converting them into a single three-valued enum which avoids being
able to represent the meaningless fourth possibility at all. Also, it
provides an open-ended place to add further possibilities.
The new field is very similar to the one in unix/network.c, except
that the UNIX entry for AF_UNIX sockets is missing, and in its place
is the NAMEDPIPE entry for storing the pathnames of Windows named
pipes.
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