WL#3984 (Revise locking of mysql.general_log and mysql.slow_log)

Bug#25422 (Hang with log tables)
Bug 17876 (Truncating mysql.slow_log in a SP after using cursor locks the
          thread)
Bug 23044 (Warnings on flush of a log table)
Bug 29129 (Resetting general_log while the GLOBAL READ LOCK is set causes
           a deadlock)

Prior to this fix, the server would hang when performing concurrent
ALTER TABLE or TRUNCATE TABLE statements against the LOG TABLES,
which are mysql.general_log and mysql.slow_log.

The root cause traces to the following code:
in sql_base.cc, open_table()
  if (table->in_use != thd)
  {
    /* wait_for_condition will unlock LOCK_open for us */
    wait_for_condition(thd, &LOCK_open, &COND_refresh);
  }
The problem with this code is that the current implementation of the
LOGGER creates 'fake' THD objects, like
- Log_to_csv_event_handler::general_log_thd
- Log_to_csv_event_handler::slow_log_thd
which are not associated to a real thread running in the server,
so that waiting for these non-existing threads to release table locks
cause the dead lock.

In general, the design of Log_to_csv_event_handler does not fit into the
general architecture of the server, so that the concept of general_log_thd
and slow_log_thd has to be abandoned:
- this implementation does not work with table locking
- it will not work with commands like SHOW PROCESSLIST
- having the log tables always opened does not integrate well with DDL
operations / FLUSH TABLES / SET GLOBAL READ_ONLY

With this patch, the fundamental design of the LOGGER has been changed to:
- always open and close a log table when writing a log
- remove totally the usage of fake THD objects
- clarify how locking of log tables is implemented in general.

See WL#3984 for details related to the new locking design.

Additional changes (misc bugs exposed and fixed):

1)

mysqldump which would ignore some tables in dump_all_tables_in_db(),
 but forget to ignore the same in dump_all_views_in_db().

2)

mysqldump would also issue an empty "LOCK TABLE" command when all the tables
to lock are to be ignored (numrows == 0), instead of not issuing the query.

3)

Internal errors handlers could intercept errors but not warnings
(see sql_error.cc).

4)

Implementing a nested call to open tables, for the performance schema tables,
exposed an existing bug in remove_table_from_cache(), which would perform:
  in_use->some_tables_deleted=1;
against another thread, without any consideration about thread locking.
This call inside remove_table_from_cache() was not required anyway,
since calling mysql_lock_abort() takes care of aborting -- cleanly -- threads
that might hold a lock on a table.
This line (in_use->some_tables_deleted=1) has been removed.

sql/handler.h

@@ -1035,44 +1035,6 @@ public:
   {
     cached_table_flags= table_flags();
   }
-  /*
-    Check whether a handler allows to lock the table.
-
-    SYNOPSIS
-      check_if_locking_is_allowed()
-        thd     Handler of the thread, trying to lock the table
-        table   Table handler to check
-        count   Total number of tables to be locked
-        current Index of the current table in the list of the tables
-                to be locked.
-        system_count Pointer to the counter of system tables seen thus
-                     far.
-        called_by_privileged_thread TRUE if called from a logger THD
-                                    (general_log_thd or slow_log_thd)
-                                    or by a privileged thread, which
-                                    has the right to lock log tables.
-
-    DESCRIPTION
-      Check whether a handler allows to lock the table. For instance,
-      MyISAM does not allow to lock mysql.proc along with other tables.
-      This limitation stems from the fact that MyISAM does not support
-      row-level locking and we have to add this limitation to avoid
-      deadlocks.
-
-    RETURN
-      TRUE      Locking is allowed
-      FALSE     Locking is not allowed. The error was thrown.
-  */
-  virtual bool check_if_locking_is_allowed(uint sql_command,
-                                           ulong type, TABLE *table,
-                                           uint count, uint current,
-                                           uint *system_count,
-                                           bool called_by_privileged_thread)
-  {
-    return TRUE;
-  }
-  bool check_if_log_table_locking_is_allowed(uint sql_command,
-                                             ulong type, TABLE *table);
   int ha_open(TABLE *table, const char *name, int mode, int test_if_locked);
   void adjust_next_insert_id_after_explicit_value(ulonglong nr);
   int update_auto_increment();
@@ -1196,6 +1158,7 @@ public:
    */
   int ha_external_lock(THD *thd, int lock_type);
   int ha_write_row(uchar * buf);
+  int ha_write_row_no_binlog(uchar * buf);
   int ha_update_row(const uchar * old_data, uchar * new_data);
   int ha_delete_row(const uchar * buf);