Bug: a88/45a

I seem to recall that I used the Swing file dialog for opening
files even on OS X, because the native dialog didn't support 
directory selection, or perhaps multiple file selection, or
perhaps both. As of Java 7 multiple file selection is supported;
https://developer.apple.com/library/mac/documentation/Java/Conceptual/Java14Development/07-NativePlatformIntegration/NativePlatformIntegration.html
gives a method for supporting directory selection. More seriously,
in my OS X testing it seems impossible to change directory in 
the Swing chooser on OS X, except by dragging a directory to the
dialog! Nobody else has reported this problem so perhaps it's a quirk
of my test system, but it's still a strong reason for changing to
the native dialog if possible.