Selecting file type in Export dialog has no effect on JFileChooser in OSX

[GoogleCodeExporter]

What steps will reproduce the problem?
1. click Export icon
2. select PNG, GIF, or JPG from dialog
3. click Export button

What is the expected output? What do you see instead?
User can type in any name. If no extension supplied, none added. If we code a 
way to add an extension, the file/replace behavior is broken (e.g., enter 
"test" and if test exists, user prompted if they want to replace "test" from 
within FileDialog, then outside FileDialog, we'd add e.g., ".png" and save to 
"test.png" which may or may not exist)

This wil require native coding of a filechooser which means additional 
maintenance for OSX platforms.

Please use labels and text to provide additional information.

Original issue reported on code.google.com by shimniok on 1 Nov 2012 at 5:13