Fix #47!  Add doubled modal popup for weird OSX issue

Sorry, should have done the branch management after this pull, but alas!  A duplicate pull request appears.

@SethTisue Please take a look and see if I did anything big and goofy.

As a side question, should we centralize isMac into Version.scala (or maybe somewhere else)? This is now the third place we look at this system property for exactly this purpose in exactly this way