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/mysql_priv.h

@@ -944,6 +944,7 @@ void mysql_parse(THD *thd, const char *inBuf, uint length,
 
 bool mysql_test_parse_for_slave(THD *thd,char *inBuf,uint length);
 bool is_update_query(enum enum_sql_command command);
+bool is_log_table_write_query(enum enum_sql_command command);
 bool alloc_query(THD *thd, const char *packet, uint packet_length);
 void mysql_init_select(LEX *lex);
 void mysql_reset_thd_for_next_command(THD *thd);
@@ -1123,7 +1124,8 @@ TABLE_SHARE *get_table_share(THD *thd, TABLE_LIST *table_list, char *key,
                              uint key_length, uint db_flags, int *error);
 void release_table_share(TABLE_SHARE *share, enum release_type type);
 TABLE_SHARE *get_cached_table_share(const char *db, const char *table_name);
-TABLE *open_ltable(THD *thd, TABLE_LIST *table_list, thr_lock_type update);
+TABLE *open_ltable(THD *thd, TABLE_LIST *table_list, thr_lock_type update,
+                   uint lock_flags);
 TABLE *open_table(THD *thd, TABLE_LIST *table_list, MEM_ROOT* mem,
 		  bool *refresh, uint flags);
 bool reopen_name_locked_table(THD* thd, TABLE_LIST* table_list, bool link_in);
@@ -1231,6 +1233,11 @@ void reset_status_vars();
 
 /* information schema */
 extern LEX_STRING INFORMATION_SCHEMA_NAME;
+/* log tables */
+extern LEX_STRING MYSQL_SCHEMA_NAME;
+extern LEX_STRING GENERAL_LOG_NAME;
+extern LEX_STRING SLOW_LOG_NAME;
+
 extern const LEX_STRING partition_keywords[];
 ST_SCHEMA_TABLE *find_schema_table(THD *thd, const char* table_name);
 ST_SCHEMA_TABLE *get_schema_table(enum enum_schema_tables schema_table_idx);
@@ -1557,6 +1564,10 @@ bool open_system_tables_for_read(THD *thd, TABLE_LIST *table_list,
 void close_system_tables(THD *thd, Open_tables_state *backup);
 TABLE *open_system_table_for_update(THD *thd, TABLE_LIST *one_table);
 
+TABLE *open_performance_schema_table(THD *thd, TABLE_LIST *one_table,
+                                     Open_tables_state *backup);
+void close_performance_schema_table(THD *thd, Open_tables_state *backup);
+
 bool close_cached_tables(THD *thd, bool wait_for_refresh, TABLE_LIST *tables, bool have_lock = FALSE);
 bool close_cached_connection_tables(THD *thd, bool wait_for_refresh,
                                     LEX_STRING *connect_string,
@@ -1891,6 +1902,7 @@ MYSQL_LOCK *mysql_lock_tables(THD *thd, TABLE **table, uint count,
 #define MYSQL_LOCK_NOTIFY_IF_NEED_REOPEN        0x0004
 #define MYSQL_OPEN_TEMPORARY_ONLY               0x0008
 #define MYSQL_LOCK_IGNORE_GLOBAL_READ_ONLY      0x0010
+#define MYSQL_LOCK_PERF_SCHEMA                  0x0020
 
 void mysql_unlock_tables(THD *thd, MYSQL_LOCK *sql_lock);
 void mysql_unlock_read_tables(THD *thd, MYSQL_LOCK *sql_lock);