Merge a change from MySQL (looks like this is against 5.0 but they later
merged it to 5.1):

  ------------------------------------------------------------
  revno: 1810.3846.1
  committer: Alexey Botchkov <holyfoot@mysql.com>
  branch nick: 31435
  timestamp: Tue 2008-11-11 14:42:32 +0400
  message:
    Bug#31435 ha_innodb.cc:3983: ulint convert_search_mode_to_innobase(ha_rkey_function): Asse 
        I think we don't need to issue an error statement in the convert_search_mode_to_innobase().
        Returning the PAGE_CUR_UNSUPP value is enough as allows to handle this
        case depending on the requirements.
    
    per-file comments:
      sql/ha_innodb.cc 
    Bug#31435 ha_innodb.cc:3983: ulint convert_search_mode_to_innobase(ha_rkey_function): Asse 
         no error issued in convert_search_mode_to_innobase.
         ha_innobase::records_in_range() returns HA_POS_ERROR if search mode isn't supported.
  modified:
    sql/ha_innodb.cc