<Swing Dev> [8] Review request for 7173873 JFrame.setDefaultCloseOperation(EXIT_ON_CLOSE) will never lead to SE if EXIT_ON_CLOSE is already set

[Alexander Scherbatiy]

bug: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7173873
webrev: http://cr.openjdk.java.net/~alexsch/7173873/webrev.00

The fix checks the EXIT_ON_CLOSE operation by system security manager 
even the same value has been already set.

Thanks,
Alexandr.