pgsql: Make \d order a table's check constraints by constraint name

Log Message:
-----------
Make \d order a table's check constraints by constraint name instead
of the text of the constraint condition. Per Chris K-L, though I didn't
use his patch exactly.

Modified Files:
--------------
pgsql/src/bin/psql:
describe.c (r1.127 -> r1.128)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/describe.c.diff?r1=1.127&r2=1.128)