Test SVG EXPORT

This is a preliminary work, nearly done for the svg export.
Final PR will have clean files, those commits are dirty.

@kangax if you can help me with the 2 failing tests, from polygon and polyline, i searche all fabric.js file and there is no trace of that error in case of missing points.
I even searched on past revision, but it looks like that function never existed.

I'm commenting some lines to explain you some decisions.
Hm, you sure? Did you check if images still render fine?