Problem:

We maintain two rb trees in each dict_table_t.  The foreign_rbt must be in
sync with foreign_list.  The referenced_rbt must be in sync with
referenced_list. There is one function which checks this consistency and it
failed, resulting in an assert failure.

The root cause of the problem was identified that the search order was 
lost in the referenced_rbt.  This is because while renaming the table,
we didn't not refresh this referenced_rbt.

Solution:

When a foreign key is renamed, we must delete and re-insert into both
foreign_rbt and referenced_rbt.  

rb#6412 approved by Jimmy.