Add a user define value "tracker updates count per second"

[bordercollie]

I found a problem that if you have too many torrents (eg. more than 2000) in your utorrent, utorrent would have difficult in update trackers.

utorrent update trackers too slow...

[moogly]

I found a problem that if you have too many tabs (eg more than 2000) in your Firefox, Firefox would have difficult in refresh tabs.