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.

youtube-dl

@@ -1724,7 +1724,7 @@ class VimeoIE(InfoExtractor):
 	"""Information extractor for vimeo.com."""
 
 	# _VALID_URL matches Vimeo URLs
-	_VALID_URL = r'(?:https?://)?(?:(?:www|player).)?vimeo\.com/(?:video/)?([0-9]+)'
+	_VALID_URL = r'(?:https?://)?(?:(?:www|player).)?vimeo\.com/(?:groups/[^/]+/)?(?:videos?/)?([0-9]+)'
 
 	def __init__(self, downloader=None):
 		InfoExtractor.__init__(self, downloader)