Support more YouTube URLs

The regular expression is also more strict, yet accepts the
youtu.be short URLs and user page URLs.

weboob/backends/youtube/test.py

@@ -29,4 +29,5 @@ class YoutubeTest(BackendTest):
         v = l[0]
         self.backend.fillobj(v, ('url',))
         self.assertTrue(v.url and v.url.startswith('http://'), 'URL for video "%s" not found: %s' % (v.id, v.url))
+        assert self.backend.get_video(v.shorturl)
         self.backend.browser.openurl(v.url)