Fixes build in uninstalled GStreamer setup or with GStreamer having
been installed in a different prefix.

Rather than reparenting the clutter embed into the fullscreen
window and back, we now create a new embed for fullscreen mode
and move the clutter sink actor into it.  At some point, clutter
stopped being able to handle events when the embed widget gets
reparented.

If the scale loses focus immediately after receiving a button press
event, it shouldn't think the user is still dragging the slider.
This happens when button presses go through the scale to the toolbar.

GtkScale has the right behaviour now.  Keep the workaround for
older versions.

Returning GValues as boxed types through
rb_signal_accumulator_value_handled adds an extra copy that
we can't clean up.  Not a problem for basic types, but
for objects and strings it causes leaks.  Instead, return the
values as pointers.

GApplication doesn't provide a means to do this, so check if the
app is running by creating a dbus proxy for it before registration.

'caps' is created with gst_caps_from_string so it must be unref'ed
when it's no longer used.

https://bugzilla.gnome.org/show_bug.cgi?id=678208

g_string_new_len copies the data rather than taking ownership
of it.  Manually allocate GStrings and assign the buffers to
them instead.

More huge leaks.

More huge leaks.

When a track gets skipped before it even starts playing, the
buffered tag lists that would have been processed when it started
need to be cleaned up in the dispose function.

this fixes a reasonably large leak on each track change.