Problem: we may create a deadlock committing changes in the mysql_alter_table() when 
LOCK_open is set. Moreover, "in some variants of the ALTER TABLE commit
happens earlier, outside of LOCK_open, in other later - inside. It's no good, a storage 
engine code that is called in between could expect a consistency - either there is a 
transaction or there is not".
Fix: move the commit to happen earlier and outside of the LOCK_open.