[PATCH FOR APPROVAL]: Backport regression fix from OpenJDK7 (6648816)

[Andrew John Hughes]

The following fix for AccessControlContext was applied to OpenJDK7 and
proprietary JDK6u10 but not backported to OpenJDK6.  It's a trivial
fix, which prevents a NullPointerException being thrown when
-Djava.security.debug=failure

See: http://icedtea.classpath.org/bugzilla/show_bug.cgi?id=364 and
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6648816

The webrev for the backport is here:

http://cr.openjdk.java.net/~andrew/6648816/webrev.01/

Ok to push this?

Thanks,
-- 
Andrew :-)

Free Java Software Engineer
Red Hat, Inc. (http://www.redhat.com)

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