MacGui: merged the two browerFile methods.

git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@6582 b64f7644-9d1e-0410-96f1-a4d463321fa5
MacGui: start a new scan from a drag & drop only if there isn't already one. Put back the outputPanel init I had accidentally moved after the HBCore one.

git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@6583 b64f7644-9d1e-0410-96f1-a4d463321fa5