<Swing Dev> RfR JDK-8134116, Add more comprehensive fix and regression test for JDK-8133897

[Pete Brunet]

Please review this patch:
http://cr.openjdk.java.net/~ptbrunet/JDK-8134116/webrev.02/

The issue raised/fixed in 8133897 and now resolved in a better fashion
in this patch is caused by an override of the functionality of
JTabbedPane such that its Page inner class title field is not kept up to
date by the overriding code. When the Page title field is empty
getTitleAt is now called so that the overridden getTitleAt will provide
the title.

Bug: https://bugs.openjdk.java.net/browse/JDK-8134116

Pete