vimeo: Tweak the regexp to allow some extended URLs from vimeo.

vimeo: Tweak the regexp to allow some extended URLs from vimeo.

This, in particular, lets me grab the videos from the beginners channel with
URLs like:

    http://vimeo.com/groups/fivebyfive/videos/22648611

Note that the regexp *will* break for other URLs that we don't know about
and that's on purpose: we don't want to accidentally grab videos that would
be passed on to other information extractors.