The current enabled/disabled state of button is inconsistent with it's intended (if any) behavour

At the moment, following is true:

1. setting disabled="disabled" in DOM doesn't affect creation of button
2. setting options.disabled to true doesn't create a disabled state, only a call to _setOption will trigger what options.disabled is set to (via $.Widget.prototype._setOption()).
   
3. options.disabled is undocumented, though _init is reacting to it, though in limited way
4. calling .button("disable") doesn't set disabled="disabled" in DOM, and vice versa with .button("enable").
   

I think above should be taken care of.