[MDEV-10570] Add Flashback support

==== Description ====

Flashback can rollback the instances/databases/tables to an old snapshot.
It's implement on Server-Level by full image format binary logs (--binlog-row-image=FULL), so it supports all engines.
Currently, it’s a feature inside mysqlbinlog tool (with --flashback arguments).

Because the flashback binlog events will store in the memory, you should check if there is enough memory in your machine.

==== New Arguments to mysqlbinlog ====

--flashback (-B)
It will let mysqlbinlog to work on FLASHBACK mode.

==== New Arguments to mysqld ====

--flashback

Setup the server to use flashback. This enables binary log in row mode
and will enable extra logging for DDL's needed by flashback feature

==== Example ====

I have a table "t" in database "test", we can compare the output with "--flashback" and without.

#client/mysqlbinlog /data/mysqldata_10.0/binlog/mysql-bin.000001 -vv -d test -T t --start-datetime="2013-03-27 14:54:00" > /tmp/1.sql
#client/mysqlbinlog /data/mysqldata_10.0/binlog/mysql-bin.000001 -vv -d test -T t --start-datetime="2013-03-27 14:54:00" -B > /tmp/2.sql

Then, importing the output flashback file (/tmp/2.log), it can flashback your database/table to the special time (--start-datetime).
And if you know the exact postion, "--start-postion" is also works, mysqlbinlog will output the flashback logs that can flashback to "--start-postion" position.

==== Implement ====

1. As we know, if binlog_format is ROW (binlog-row-image=FULL in 10.1 and later), all columns value are store in the row event, so we can get the data before mis-operation.

2. Just do following things:

  2.1 Change Event Type, INSERT->DELETE, DELETE->INSERT.
  For example:
    INSERT INTO t VALUES (...)  ---> DELETE FROM t WHERE ...
    DELETE FROM t ... ---> INSERT INTO t VALUES (...)

  2.2 For Update_Event, swapping the SET part and WHERE part.
  For example:
    UPDATE t SET cols1 = vals1 WHERE cols2 = vals2
    --->
    UPDATE t SET cols2 = vals2 WHERE cols1 = vals1

  2.3 For Multi-Rows Event, reverse the rows sequence, from the last row to the first row.
  For example:
    DELETE FROM t WHERE id=1; DELETE FROM t WHERE id=2; ...; DELETE FROM t WHERE id=n;
    --->
    DELETE FROM t WHERE id=n; ...; DELETE FROM t WHERE id=2; DELETE FROM t WHERE id=1;

  2.4 Output those events from the last one to the first one which mis-operation happened.
  For example:

1 files changed, 4 insertions, 3 deletions

diff --git a/sql/sys_vars.cc b/sql/sys_vars.cc
index 56913092354..057e18f8f06 100644
--- a/sql/sys_vars.cc
+++ b/sql/sys_vars.cc
@@ -449,16 +449,17 @@ static bool binlog_format_check(sys_var *self, THD *thd, set_var *var)
   /*
     MariaDB Galera does not support STATEMENT or MIXED binlog format currently.
   */
-  if (WSREP(thd) && var->save_result.ulonglong_value != BINLOG_FORMAT_ROW)
+  if ((WSREP(thd) || opt_support_flashback) &&
+      var->save_result.ulonglong_value != BINLOG_FORMAT_ROW)
   {
     // Push a warning to the error log.
     push_warning_printf(thd, Sql_condition::WARN_LEVEL_WARN, ER_UNKNOWN_ERROR,
-                        "MariaDB Galera does not support binlog format: %s",
+                        "MariaDB Galera and flashback does not support binlog format: %s",
                         binlog_format_names[var->save_result.ulonglong_value]);
 
     if (var->type == OPT_GLOBAL)
     {
-      WSREP_ERROR("MariaDB Galera does not support binlog format: %s",
+      WSREP_ERROR("MariaDB Galera and flashback does not support binlog format: %s",
                   binlog_format_names[var->save_result.ulonglong_value]);
       return true;
     }