Multimedia stock icons namechange

[Christian Schaller <uraeus linuxrising org>]

Hi,
Everyone who is working on a GNOME or GTK+ application that uses media
player icons, like forward/back etc. should look at the following bug:
http://bugzilla.gnome.org/show_bug.cgi?id=117458

With this change we now have standarized names for these buttons to
allow them to be consistently themed across applictions. Make sure to
have your own application use the same names.

Christian