Update section on NFS

Attached is a patch that rewrites the section on NFS.  The old section
was ancient and didn't seem very helpful.

AFAIK, the only strict requirement for using NFS with PostgreSQL is the
hard mount.  Anything else we should mention?

I also reorganized the sectioning so that information about other file
systems can be added more easily.

Can anyone suggest some succinct advice on what file systems are
supported on Windows (see XXX in the patch)?

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services