pgsql: Allow uuid_in() to parse a wider variety of variant input formats

Log Message:
-----------
Allow uuid_in() to parse a wider variety of variant input formats for the UUID
data type. This patch takes the approach of allowing an optional hyphen after
each group of four hex digits.

Author: Robert Haas <robertmhaas@gmail.com>

Modified Files:
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pgsql/doc/src/sgml:
datatype.sgml (r1.230 -> r1.231)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/datatype.sgml?r1=1.230&amp;r2=1.231)
pgsql/src/backend/utils/adt:
uuid.c (r1.7 -> r1.8)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/uuid.c?r1=1.7&amp;r2=1.8)