mtree module still has a few issues:
- parameters mt_allow_duplicates/mt_ignore_duplicates seem to have global
meaning affecting all mtrees.
- if db_table module param is used instead of mtree module params, all
trees in the table must have either int or string values
my suggestion is that in the future db_table module param is removed and
all relevant other module parameters is moved to parameters of mtree
module parameter.
-- juha