Revert "Always go for the Command key binding on the mac."

With apologies to @monkeyiq, this change appears to make arrow keys stop working on Mac OSX (10.8).  By which I mean that with the change, the arrow keys only scroll the viewport, rather than move the selection as was the previous behavior.

This reverts commit 0e186efed1fa794972d3203ec4e99f48fc6d7c82.