Fixed a reappeared old bug with mod_offline and MAM.
Added a second place from which invitation_sent is activated.
Made mod_mam_muc:restore_dump_file/3 more verbose in error reporting.
Made mod_mam:restore_dump_file/3 more verbose in error reporting.
Fixed wrong calculations in mod_mam_odbc_async_pool_writer:is_overloaded/1.