[8u] RFR 8129940: JRadioButton does not honor non-standard FocusTraversalKeys

[Zhengyu Gu]

I would like to backport this patch to openjdk8u for parity with Oracle 
8u311.

The original bug: https://bugs.openjdk.java.net/browse/JDK-8129940
The original patch: 
http://hg.openjdk.java.net/jdk9/jdk9/jdk/rev/fbf897c33625

8u patch: http://cr.openjdk.java.net/~zgu/JDK-8129940-8u/webrev.00/

The jdk9 patch does not apply cleanly, but only conflict is copyright 
year of BasicRadioButtonUI.java file.

Test:
   Included FocusTraversal/FocusTraversal.java test fails without patch 
and passes with it on Linux x86_64

Thanks,

-Zhengyu