Netmask bug
change db update version number
Merge pull request #319 from NielsZeilemaker/fix_is_valid_ip

Netmask bug
fix a mistake of using dict
small fix
make task management methods thread safe
Merge pull request #318 from whirm/task_manager

cancel_pending_task should always be called from the reactor
Merge pull request #320 from LipuFei/fix-db

Try to fix db problem