27480: Extend CREATE TEMPORARY TABLES privilege to
allow temp table operations).

Got rid of extra call to open_temporary_tables() during
HANDLER OPEN introduced by one of previous patches.
This call to open_temporary_tables() was necessary for 
privilege checking. It became possible to remove it by 
moving privilege check inside of mysql_ha_open() call

Also all HANDLER commands were converted to using Sql_cmd
infrastructure.