Review request for 7130360: [macosx] Packed JInternalFrame invisible on Aqua L&F

[Alexander Potochkin]

Hello

Please review the following fix:
http://cr.openjdk.java.net/~alexp/7130360/webrev.00/

the bug's description is here:
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7130360

AquaInternalFrameUI.minimumLayoutSize() doesn't override any method
and is never called from any other classes, so I removed it

The LayoutManager in BasicInternalFrameUI is private,
so I overrode getPreferredSize() method to make sure that it never 
returns the size less then the minimal size

Thanks
alexp