Plugin:
- get info about play state, URL etc back from viewer to the plugin
- support all <embed> and <object> attributes that the legacy plugins support
- there still seem to be some unnecessary symbols exported in the plugin .so's
- use peer-2-peer DBUS instead of session bus
- (maybe) use libdbus directly instead of dbus-glib
- unify playlist handling into the viewer (is it possible to write a gstreamer element
  that handles the playlist internally?)
- make StreamAsFile use async calls; need to keep a link to the file around!!
- put back narrowspace URL extension parsing
- use nsCOMPtr<> once the linking has been figured out (libxpcomglue_s)
- invert DBUS-OpenStream/NPN_GetURL order: this is necessary so we can push the real stream URI
  to the viewer (for use as base uri for redirects)