bzr commit into mysql-6.0 branch (staale.smedseng:2938) Bug#22891

[Staale Smedseng]

#At file:///export/home/tmp/ss156133/z/b22891-60-bugteam/

 2938 Staale Smedseng	2008-11-20 [merge]
      A fix for Bug#22891 "session level max_allowed_packet can be
      set but is ignored".
                                        
      This patch makes @@session.max_allowed_packed and
      @@session.net_buffer_length read-only as suggested in the bug
      report. The user will have to use SET GLOBAL (and reconnect)
      to alter the session values of these variables.
                                  
      The error string ER_VARIABLE_IS_READONLY is introduced.
                                  
      Tests are modified accordingly.
      
      Merge into mysql-6.0-bugteam.