[7u6] Please review my fix for 7184951: [macosx] Exception at java.awt.datatransfer on headless mode (only in GUI session)

[Alexander Zuev]

Hello,

   please review my fix 7184951: [macosx] Exception at 
java.awt.datatransfer on headless mode (only in GUI session)
   CR description can be found here: 
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7184951

   Webrev with the proposed change can be seen here: 
http://cr.openjdk.java.net/~kizune/7184951/webrev.00

   The problem here lays somewhere deep in the Toolkit life cycle on
Mac OS X - at the time we initialize datatransfer the 
Toolgit.getDefaultToolkit() returns an LWCToolkit instance and later 
when we trying to use it it returns HeadlessToolkit. That's definitely
wrong but at this stage it's too risky to fiddle with the life cycle
itself so this is a hotfix that deals with the fallout of the actual
error. The fix for jdk8 should be different.

With best regards,
Alex