recent: Fix warning for videos without known mime-types
When playing http://samples.mplayerhq.hu/yuv4mpeg2/example.y4m.bz2 the recent plugin would warn that:
(totem:2254517): Gtk-WARNING **: 19:27:38.141: Attempting to add 'file:///home/hadess/Videos/example.y4m' to the list of recently used resources, but no MIME type was defined
(totem:2254517): Totem-WARNING **: 19:27:38.141: Couldn't add recent file for 'file:///home/hadess/Videos/example.y4m'
Use our app-specific mime-type to handle those cases.
Edited by Bastien Nocera