MacGui: Yet another x264 advanced controller change...rewording the b-adapt pop up...

MacGui: Yet another x264 advanced controller change...rewording the b-adapt pop up menu items to read "Off", "Fast", "Optimal" instead of 0, 1, 2. The whole "optimal gets progressively slower as you increase the max permitted length of b-frame chains" part will be explained in the tool tip, when those all get moved from xib to code.

git-svn-id: svn://localhost/HandBrake/trunk@2162 b64f7644-9d1e-0410-96f1-a4d463321fa5