Fix for BUG#9412: Triggers: should have trigger privilege.

Implement table-level TRIGGER privilege to control access to triggers.
Before this path global SUPER privilege was used for this purpose, that
was the big security problem.

In details, before this patch SUPER privilege was required:
  - for the user at CREATE TRIGGER time to create a new trigger;
  - for the user at DROP TRIGGER time to drop the existing trigger;
  - for the definer at trigger activation time to execute the trigger (if the
    definer loses SUPER privilege, all its triggers become unavailable);

This patch changes the behaviour in the following way:
  - TRIGGER privilege on the subject table for trigger is required:
    - for the user at CREATE TRIGGER time to create a new trigger;
    - for the user at DROP TRIGGER time to drop the existing trigger;
    - for the definer at trigger activation time to execute the trigger
      (if the definer loses TRIGGER privilege on the subject table, all its
      triggers on this table become unavailable).
  - SUPER privilege is still required:
    - for the user at CREATE TRIGGER time to explicitly set the trigger
      definer to the user other than CURRENT_USER().

When the server works with database of the previous version (w/o TRIGGER
privilege), or if the database is being upgraded from the previous versions,
TRIGGER privilege is granted to whose users, who have CREATE privilege.

mysql-test/r/trigger-grant.result

@@ -7,12 +7,57 @@ DROP DATABASE IF EXISTS mysqltest_db1;
 CREATE DATABASE mysqltest_db1;
 CREATE USER mysqltest_dfn@localhost;
 CREATE USER mysqltest_inv@localhost;
-GRANT SUPER ON *.* TO mysqltest_dfn@localhost;
 GRANT CREATE ON mysqltest_db1.* TO mysqltest_dfn@localhost;
 
 ---> connection: wl2818_definer_con
 CREATE TABLE t1(num_value INT);
 CREATE TABLE t2(user_str TEXT);
+
+---> connection: default
+GRANT INSERT, DELETE ON mysqltest_db1.t1 TO mysqltest_dfn@localhost;
+GRANT INSERT, DELETE ON mysqltest_db1.t2 TO mysqltest_dfn@localhost;
+
+---> connection: default
+GRANT SUPER ON *.* TO mysqltest_dfn@localhost;
+
+---> connection: wl2818_definer_con
+CREATE TRIGGER trg1 AFTER INSERT ON t1
+FOR EACH ROW
+INSERT INTO t2 VALUES(CURRENT_USER());
+ERROR 42000: TRIGGER command denied to user 'mysqltest_dfn'@'localhost' for table 't1'
+
+---> connection: default
+GRANT TRIGGER ON mysqltest_db1.t1 TO mysqltest_dfn@localhost;
+
+---> connection: wl2818_definer_con
+CREATE TRIGGER trg1 AFTER INSERT ON t1
+FOR EACH ROW
+INSERT INTO t2 VALUES(CURRENT_USER());
+
+---> connection: default
+REVOKE TRIGGER ON mysqltest_db1.t1 FROM mysqltest_dfn@localhost;
+
+---> connection: wl2818_definer_con
+DROP TRIGGER trg1;
+ERROR 42000: TRIGGER command denied to user 'mysqltest_dfn'@'localhost' for table 't1'
+
+---> connection: wl2818_definer_con
+INSERT INTO t1 VALUES(0);
+ERROR 42000: TRIGGER command denied to user 'mysqltest_dfn'@'localhost' for table 't1'
+
+---> connection: default
+GRANT TRIGGER ON mysqltest_db1.t1 TO mysqltest_dfn@localhost;
+
+---> connection: wl2818_definer_con
+INSERT INTO t1 VALUES(0);
+DROP TRIGGER trg1;
+DELETE FROM t1;
+DELETE FROM t2;
+
+---> connection: default
+REVOKE SUPER ON *.* FROM mysqltest_dfn@localhost;
+
+---> connection: wl2818_definer_con
 CREATE TRIGGER trg1 AFTER INSERT ON t1
 FOR EACH ROW
 INSERT INTO t2 VALUES(CURRENT_USER());
@@ -175,6 +220,17 @@ CREATE DEFINER='mysqltest_inv'@'localhost'
   TRIGGER trg1 BEFORE INSERT ON t1
 FOR EACH ROW
 SET @new_sum = 0;
+ERROR 42000: Access denied; you need the SUPER privilege for this operation
+
+---> connection: default
+use mysqltest_db1;
+GRANT SUPER ON *.* TO mysqltest_dfn@localhost;
+
+---> connection: wl2818_definer_con
+CREATE DEFINER='mysqltest_inv'@'localhost'
+  TRIGGER trg1 BEFORE INSERT ON t1
+FOR EACH ROW
+SET @new_sum = 0;
 CREATE DEFINER='mysqltest_nonexs'@'localhost'
   TRIGGER trg2 AFTER INSERT ON t1
 FOR EACH ROW
@@ -182,7 +238,6 @@ SET @new_sum = 0;
 Warnings:
 Note	1449	There is no 'mysqltest_nonexs'@'localhost' registered
 INSERT INTO t1 VALUES(6);
-ERROR 42000: Access denied; you need the SUPER privilege for this operation
 SHOW TRIGGERS;
 Trigger	Event	Table	Statement	Timing	Created	sql_mode	Definer
 trg1	INSERT	t1	SET @new_sum = 0	BEFORE	NULL		mysqltest_inv@localhost