OC-5: Use Toolkit.getMenuShortcutKeyMask() for menu accelerator

    This follows the recommendations in the Apple java guidelines.
OC-6: Use java.awt.FileDialog instead of JFileChooser

    Per the Apple native Java guidelines. Counter-intuitively,
    FileDialog is a better native control on the Mac.
OC-6: Switch "Save As" dialog to FileDialog as well

    On Mac, at least, FileDialog handles collisions in a sane way.
OC-6: Fix: segment pane didn't always update when opening a file

    This became common after the switch to FileDialog.  I fixed it
    by moving the call to JScollPane.setViewportView() earlier, to
    before the new segments are added to the table. My theory is that
    this ensures the revalidation logic is triggered correctly.
Disable menu mnemonics on the Mac
Minor cleanup
Add platform and JVM information to the Help > About box