Partitioning didn't store the name of default storage engine for partitions
in the frm file - it only store the typecode. Typecodes aren't stable, and
might vary depending on the order in which storage engines are loaded (can
be changed even from my.cnf without recompilation).

As a temporary workaround for 5.5, we hard-code Aria's typecode, to make sure it
never changes.