renderer: Minor doc fix
renderer: Set track info for non-http uris

(Partially) fixes 7.3.53.2

https://bugzilla.gnome.org/show_bug.cgi?id=709170
Fix AbsoluteCounterPosition to match UPnP spec

UPnP AV Transport Specification v1.01 states that the
AbsoluteCounterPosition state variable is a signed value, where as the
xml document has it as an unsigned value.  Rygel stores the
AbsoluteCounterPosition internally as an signed value.

https://bugzilla.gnome.org/show_bug.cgi?id=709190