MacGui: switches the x264 option widgets for mixed-refs, weightb, brdo, bime, b-pyram...

MacGui: switches the x264 option widgets for mixed-refs, weightb, brdo, bime, b-pyramid, no-dct-decimate, and no-fast-pskip to be checkboxes, which makes more sense than popup buttons for booleans.

I've never worked with switches before, so hopefully I didn't break anything. Also never checked in this many GUI changes at once. So maybe I did break something =)

git-svn-id: svn://localhost/HandBrake/trunk@594 b64f7644-9d1e-0410-96f1-a4d463321fa5