Don't block main thread in _seek()
Don't block main thread in _seek()

Instead keep hold of the last seek request and apply it
when we've been told that the previous one finished, or
apply it straight away if the previous seek took longer than
1/10th of a second.

https://bugzilla.gnome.org/show_bug.cgi?id=588377

mediaserver2-plugins/totem-mediaserver2,mediaserver2-plugins/totem-mediaserver2