postgres2 & memsql2

add escape (quote identifiers) for the dynamic sql
so tables (collections) with special characters will work.

weed/filer/postgres2/postgres2_store.go

@@ -48,7 +48,7 @@ func (store *PostgresStore2) initialize(createTable, user, password, hostname st
 	store.SupportBucketTable = true
 	store.SqlGenerator = &postgres.SqlGenPostgres{
 		CreateTableSqlTemplate: createTable,
-		DropTableSqlTemplate:   "drop table %s",
+		DropTableSqlTemplate: `drop table "%s"`,
 	}
 
 	sqlUrl := fmt.Sprintf(CONNECTION_URL_PATTERN, hostname, port, sslmode)