Make time interval test not dependent on intervalstyle

Fixes testing from under cartodb/lib/sql

test/CDB_CartodbfyTableTest.sql

@@ -175,7 +175,8 @@ CREATE TABLE t AS SELECT NOW()::text as created_at,
                          NOW()::text as updated_at,
                          NOW() as reftime;
 SELECT CDB_CartodbfyTableCheck('t', 'text timestamps');
-SELECT reftime-created_at, reftime-updated_at FROM t;
+SELECT extract(secs from reftime-created_at),
+       extract(secs from reftime-updated_at) FROM t;
 DROP TABLE t;
 
 -- table with existing cartodb_id field ot type text

test/CDB_CartodbfyTableTest_expect

@@ -27,7 +27,7 @@ extent|BOX(1 1,2 2)
 DROP TABLE
 SELECT 1
 text timestamps cartodbfied fine
-@ 0|@ 0
+0|0
 DROP TABLE
 SELECT 1
 text cartodb_id cartodbfied fine