MacGui: fixed the HUD background on Snow Leopard.

git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@6352 b64f7644-9d1e-0410-96f1-a4d463321fa5
MacGui: removed a couple of unused preferences keys (CheckForUpdates, DisableDvdAutoDetect, DefAdvancedx264Flags) and the empty TOOLBAR_PICTURE tab. Added a new checkbox to hide the Advanced tab.

git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@6353 b64f7644-9d1e-0410-96f1-a4d463321fa5