1. A bad error message was given when a MERGE table with an
   InnoDB child table was tried to use.

2. After selecting from a correct MERGE table and then altering
   one of the children to InnoDB, incorrect results were returned.

These bugs have been fixed with the patch for bug 26379 (Combination
of FLUSH TABLE and REPAIR TABLE corrupts a MERGE table).

For verification, I added the test case from the bug report.


mysql-test/r/merge_innodb.result:
  Bug#30491 - MERGE doesn't report error when one table is Innodb
  Added test result.
mysql-test/t/merge_innodb.test:
  Bug#30491 - MERGE doesn't report error when one table is Innodb
  Added test case.