When dumping database from a 4.x server, the mysqldump client
inserted a delimiter sign inside special commentaries of the form:
  /*!... CREATE DATABASE IF NOT EXISTS ... ;*/
During restoration that dump file was splitten by delimiter signs on
the client side, and the rest of some commentary strings was prepended
to following statements.

The 4x_server_emul test case option has been added for use with the
DBUG_EXECUTE_IF debugging macro. This option affects debug server
builds only to emulate particular behavior of a 4.x server for
the mysqldump client testing. Non-debugging builds are not affected.


mysql-test/r/mysqldump-compat.result:
  Added test case for bug #30126.
mysql-test/t/mysqldump-compat.opt:
  Added test case for bug #30126.
mysql-test/t/mysqldump-compat.test:
  Added test case for bug #30126.
sql/sql_parse.cc:
  Fixed bug #30126.
  The mysqldump client uses the "SHOW CREATE DATABASE" query to
  obtain the "CREATE DATABASE" statement from that database.
  The 4.x server doesn't recognise that query, and mysqldump
  forms the "CREATE DATABASE" statement from scratch.
  That statement was formed incorrectly.
  
  To enforce the mysqldump client to create that statement from
  scratch, debugging code has been added to the mysql_execute_command
  function: in tcase of the --loose-debug=d,4x_server_emul option,
  the server returns parse error to client to emulate old behaviour.
  
  The 4x_server_emul test case option has been added for use with the
  DBUG_EXECUTE_IF debugging macro. This option affects debug server
  builds only to emulate particular behavior of a 4.x server for
  the mysqldump client testing. Non-debugging builds are not affected.
client/mysqldump.c:
  Fixed bug #30126.
  The init_dumping_tables function has been modified to output semicolon
  outside of commentaries.