[8] Review request for 7124337: [macosx] FileDialog fails to select multiple files

[Dmitry Cherepanov]

This is a direct forward port (including a minor change for 7147066) of 
the fix to jdk8.

Bug: http://bugs.sun.com/view_bug.do?bug_id=7124337
Webrev: http://cr.openjdk.java.net/~dcherepanov/7124337/8/webrev.0/

Thanks,
Dmitry