window-tracker: Be more cautious when setting focus app

Since we started tracking non-interesting windows, we can no longer
assume that if we manage to find an app associated with the focus window,
it should appear focused - we now can find apps for docks, the DESKTOP
window etc.
To restore the old behavior, make sure that the focus window or one of
its parents is "interesting".

https://bugzilla.gnome.org/show_bug.cgi?id=722928
Bump version to 3.10.4

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