[Allocine] Support for more URLs

I noticed Allocine was supported, yet some videos kept falling back to the generic extractor:
```
$ youtube-dl http://www.allocine.fr/video/video-19550147/                                                                                                                                                                                      
[generic] video-19550147: Requesting header
WARNING: Falling back on generic information extractor.
[generic] video-19550147: Downloading webpage
[generic] video-19550147: Extracting information
ERROR: Unsupported URL: http://www.allocine.fr/video/video-19550147/; please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; type  youtube-dl -U  to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.
```

This happens for all the videos [from the "Vidéos" section](http://www.allocine.fr/video/). The extractor itself works perfectly with them, it just needed the _VALID_URL regex to include them:
```
$ ./youtube_dl/__main__.py http://www.allocine.fr/video/video-19550147/                                                                                                                              [master] 
[Allocine] 19550147: Downloading webpage
[Allocine] 19550147: Downloading XML
[download] Destination: Faux Raccord N°123 - Les gaffes de Cliffhanger-19550147.mp4
[download] 100% of 88.85MiB in 00:56
```

The only downside I've noticed is that videos hosted elsewhere (YouTube or Dailymotion) aren't supported, but that's to be expected.