Adding in a convenience feature to enable / disable buttons on buttonbar/tabbars.
Example [1] with view source enabled. Git hub diffs [2]. [1] http://people.apache.org/~mkessler/examples/FLEX-33524/app.swf [2] https://github.com/KesslerConsulting/example/commit/83905cb1a8f80bb6ac156b3d4bc6fed2a00227c2 -Mark
