#1988 - Add allow_movie_uploads option ("always", "never", or "default").

- gallery_installer, module.info, install.sql - add allow_movie_uploads variable
- movie::allow_uploads (new) - return true if allow_movie_uploads is "always" or "default" and FFmpeg found, false otherwise
- legal_file - use movie::allow_uploads instead of movie::find_ffmpeg
- Form_Uploadify - use movie::allow_uploads instead of movie::find_ffmpeg