Back out this patch because it is patched inside a later patch.

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here is a patch that allows CIDR netmasks in pg_hba.conf. It allows two
address/mask forms:

. address/maskbits, or
. address netmask (as now)

If the patch is accepted I will submit a documentation patch to cover
it.

This is submitted by agreement with Kurt Roeckx, who has worked on a
patch that covers this and other IPv6 issues.