An update that used a join of a table to itself and modified the
table on one side of the join reported the table as crashed or
updated wrong rows.

Fixed by creating temporary table for self-joined multi update statement.


mysql-test/r/myisam.result:
  A test case for BUG#21310.
mysql-test/t/myisam.test:
  A test case for BUG#21310.
sql/lock.cc:
  Exclude 'table' param from check.
sql/sql_update.cc:
  Disabling record cache for self-joined multi update statement is wrong.
  The join must only see the table as it was at the beginning of the statement.
  safe_update_on_fly check if it is safe to update first table on the fly, that is
  not creating temporary table. It is possible in case a row from this table is
  never read more than once. safe_update_on_fly now detect self-joined table and
  refuse to update this table on the fly.