Bug fixed B65-ZK-1884: The slider's value should not be greater then
maxpos after clicked its rightmost position 
http://tracker.zkoss.org/browse/ZK-1884
fine tune
minor fix slider's animation
minor fix test case
add comment
Merge branch 'B65-ZK-1884' of git://github.com/RaymondChao/zk into 7.0