Slider.html sample fixes.
Slider.html sample fixes.

1. put <input> control in test file so that back/forward buttons and form refresh work.

2. Use observe() on slider value, so that it reports programmatic modifications
   in addition to changes initiated by the user.

3. Fix "Set" buttons (on chrome 36, IE).  They need to be type=button.

Slider-dual.html and Slider-single.html still need to be updated.

Fixes #227.

redaktor/deliteful