MacGui: Rework how we get encode and queue done alerts.

MacGui: Rework how we get encode and queue done alerts.
- Add separate checkbox for system alert sound in Preferences > General > When Done (previously it was automatic only when "When Done" included the alert panel")
- System alert sound will play whenever the specified Alert When Done event occurs if its checked (this includes the Growl alerts which come up as encodes roll off of the queue) which addresses the sound part of this forum thread http://forum.handbrake.fr/viewtopic.php?f=22&t=17347#p80456. Thanks to BradleyS for the suggestion.
- Also fix an issue introduced in the multi instance queue commmit (ref 3450) where the Alert Window would come up one encode too early instead of at the end of the queue if you use the alert window for when queue is completed. This addresses forum thread http://forum.handbrake.fr/viewtopic.php?f=12&t=17367 thanks to noved for picking up on it.
- Get rid of a touch of commented code from rev 3450 which is worthless.

git-svn-id: svn://localhost/HandBrake/trunk@3461 b64f7644-9d1e-0410-96f1-a4d463321fa5