- replace @message by $message
  --> The annoying protocol line "SET @message= <value>" will disappear.
- extended description
- some examples added


mysql-test/include/show_msg.inc:
  replace @message by $message
mysql-test/include/show_msg80.inc:
  - replace @message by $message
  - extended description
  - some examples added
mysql-test/r/mysqltest.result:
  updated results
mysql-test/t/mysqltest.test:
  sub testcases for the show_msg*.inc scripts modified, because the script properties are altered