CIDR in pg_hba.conf

Looking through the TODO list I noticed this item apparently unclaimed:

* Allow CIDR format to be used in pg_hba.conf

I can look at doing this, having done similar code some years ago.

Internally, it seems the best thing to do would be to turn the /nn into a
conventional netmask of the right family. I guess I'd add a utility routine
to ip.c for that.

The syntax for pg_hba.conf would change slightly, to allow these forms:

host database user CIDR-address authentication-method
[authentication-option]
hostssl database user CIDR-address authentication-method
[authentication-option]

So in hba.c, if we found a / in the IP address, we wouldn't go looking for a
separate netmask field.

cheers

andrew