CREATE RULE may generate duplicate entries in pg_depend

If action and qual reference same object in CREATE RULE, it results in
creating duplicate entries in pg_depend for it. Doesn't pose any harm, just
unnecessarily bloats pg_depend. Reference InsertRule(). I think should be
able to avoid adding duplicate entries.

Don't know if this behaviour was discussed earlier, I didn't find it on
search.
We accidentally encountered it while enhancing a catalog check tool for
Greenplum Database.

For example (from rules test):
create table rtest_t5 (a int4, b text);
create table rtest_t7 (a int4, b text);

create rule rtest_t5_ins as on insert to rtest_t5
where new.a > 15 do
insert into rtest_t7 values (new.a, new.b);

# select classid::regclass, refobjid::regclass,* from pg_depend where
refobjid='rtest_t5'::regclass and deptype = 'n';
classid | refobjid | classid | objid | objsubid | refclassid | refobjid
| refobjsubid | deptype
------------+----------+---------+-------+----------+------------+----------+-------------+---------
pg_rewrite | rtest_t5 | 2618 | 16457 | 0 | 1259 | 16445
| 1 | n
pg_rewrite | rtest_t5 | 2618 | 16457 | 0 | 1259 | 16445
| 1 | n
pg_rewrite | rtest_t5 | 2618 | 16457 | 0 | 1259 | 16445
| 2 | n
(3 rows)

--
*Ashwin Agrawal (VMware)*