Add support for OF in row lock clauses

This adds support for statements such as `SELECT ... FOR UPDATE OF table NOWAIT` where `OF table`
could not be specified previously. Fixes #285.

mysql/select_statement_test.go

@@ -122,6 +122,11 @@ FOR UPDATE;
 SELECT table1.col_bool AS "table1.col_bool"
 FROM db.table1
 FOR SHARE NOWAIT;
+`)
+	testutils.AssertStatementSql(t, SELECT(table1ColBool).FROM(table1).FOR(UPDATE().OF(table1).NOWAIT()), `
+SELECT table1.col_bool AS "table1.col_bool"
+FROM db.table1
+FOR UPDATE OF table1 NOWAIT;
 `)
 }