make relation lookup behavior consistent within Spark SQL

cloud0fan=# create schema s1;
CREATE SCHEMA
cloud0fan=# SET search_path TO s1;
SET
cloud0fan=# create table s1.t (i int);
CREATE TABLE
cloud0fan=# insert into s1.t values (1);
INSERT 0 1

# access table with qualified name
cloud0fan=# select * from s1.t;
 i 
---
 1
(1 row)

# access table with single name
cloud0fan=# select * from t;
 i 
---
 1
(1 rows)

# create a temp view with conflicting name
cloud0fan=# create temp view t as select 2 as i;
CREATE VIEW

# same as spark, temp view has higher proirity during resolution
cloud0fan=# select * from t;
 i 
---
 2
(1 row)

# DROP TABLE also resolves temp view first
cloud0fan=# drop table t;
ERROR:  "t" is not a table

# DELETE also resolves temp view first
cloud0fan=# delete from t where i = 0;
ERROR:  cannot delete from view "t"