Added requestRenderAllBound

[durga598]

As requestRenderAllBound is undefined in _initStatic method of fabric.Canvas class initialize method. Here is jsfiddle.

[asturur]

Hi Durga, i m fine with this change.
I did not see the utility in first place, but at the end it can be useful too if you have multiple callback finishing very near in time.

Just to be clear to whoever read this PR, the bound method are just a typing save utility to avoid putting in callbacks

this.loadSomething(canvas.renderAll.bind(canvas))

that becomes:

this.loadSomething(canvas.renderAllBound)