gst-player: take a reference on the player when adding an idle function
gst-player: take a reference on the player when adding an idle function

When adding an idle function that uses the player object, add a reference
to the object to ensure it is still valid when the idle function is called.

GNOME/clutter-gst,GNOME/clutter-gst,GNOME/clutter-gst,lubosz/clutter-gst,ystreet/clutter-gst,ystreet/clutter-gst,ystreet/clutter-gst,lubosz/clutter-gst,ystreet/clutter-gst,lubosz/clutter-gst,GNOME/clutter-gst