Try to cast TEXT typed updated_at and created_at if present

If the cast fails we'll still rename those fields and create
new ones. See #27 (cartodb_id is still not done)

test/CDB_CartodbfyTableTest_expect

@@ -25,5 +25,9 @@ CREATE TRIGGER
 trigger-protected the_geom cartodbfied fine
 extent|BOX(1 1,2 2)
 DROP TABLE
+SELECT 1
+text timestamps cartodbfied fine
+@ 0|@ 0
+DROP TABLE
 DROP FUNCTION
 DROP FUNCTION