KEY NO 0 FOR TABLE IN ERROR LOG 

With the changes made by the patches for Bug#11751388 and
Bug#11784056, concurrent reads are allowed while secondary
indexes are created in InnoDB. This means that the metadata
lock on the affected table is not upgraded to exclusive
until the .FRM is updated at the end of ALTER TABLE processing.

The problem was that if this lock upgrade failed for some
reason (e.g. timeout), the index information in the server
and inside InnoDB would be out of sync. This would happen
since the add index operation already was committed inside 
InnoDB but the table metadata inside the server had not been
updated yet.

This patch fixes the problem by (for now) reverting the
effects of the patches for Bug#11751388 and Bug#11784056.
Concurrent reads will now again be blocked during creation
of secondary indexes in InnoDB.

Test case added to innodb_mysql_lock.test.