[Nimbus] Code to globally set slider's thumb background doesn't work as specified

Attached is the example. This little example is a modification of a demo written by Jasper Potts. It shows two problems:

1. UIManager.put() is supposed to work, but I had to use UIManager.getLookAndFeelDefaults().put, even though I had already set the L&F.

2. In order to the get background painter for the thumb to work, I couldn't just set the Slider:SliderThumb.background property (as specified), I had to set the seven keys for the background states.

See the example for more info.