* src/gen_mod.erl: First store module options in ETS and Mnesia,

* src/gen_mod.erl: First store module options in ETS and Mnesia,
then start the module. In case of failure, remove options from
ETS. Until now the module was started before the options were
stored in database, and some modules started incorrectly because
they couldn't access the options from database; for instance
mod_muc_room required this for reading max_users option.

* src/mod_muc/mod_muc_room.erl: Include the value of max_users
service option and the current max_users room option in the list
of allowed room limit values.

SVN Revision: 1685