T_CustomScan on ExplainTargetRel

Hello,

The attached obvious patch adds T_CustomScan on case-switch of
ExplainTargetRel() that was oversight.

It looked like working, but what it did was just printing referenced
name, instead of table name.

postgres=# explain select ctid, * from t0 hoge where ctid > '(50,0)'::tid;
QUERY PLAN
------------------------------------------------------------------------
Custom Scan (ctidscan) on hoge (cost=0.00..100.00 rows=3333 width=43)
Filter: (ctid > '(50,0)'::tid)
ctid quals: (ctid > '(50,0)'::tid)
(3 rows)

This patch fixes up this behavior, as like other *Scan nodes are doing.

postgres=# explain select ctid, * from t0 hoge where ctid > '(50,0)'::tid;
QUERY PLAN
-------------------------------------------------------------
Seq Scan on t0 hoge (cost=0.00..209.00 rows=3333 width=43)
Filter: (ctid > '(50,0)'::tid)
(2 rows)

Thanks,
--
NEC OSS Promotion Center / PG-Strom Project
KaiGai Kohei <kaigai(at)ak(dot)jp(dot)nec(dot)com>