Tone down FlashVideo::Site::Channel5's greediness

FlashVideo::Site::Channel5 claims it can_handle() anything containing brightcode videos, then proceeds to die when it bites off something FlashVideo::Site::Brightcove can chew better, for example http://ww3.tvo.org/video/173822/secret-life-chaos.

This fixes tvo.org and probably alot of others, the brightcove plugin is just as greedy but works as a generic plugin. (Untested) FlashVideo::URLFinder::_find_package_url should prioritize Channel5.pm for channel5. If not, can_handle_generic() seems like a good idea.