Various fixes

Various fixes
misc.js -When we group SVG's elements we should return always a pathgroup, it semplifies the logic after.
text.class.js -Fixes text position broken from 1.4.x onwards in svg parsing.
I never looked at it, so it is a trial and error fix.
Anyway originX ( and so text-anchor from the svg properties ) was not correctly supported.
Something in native rendering is not fine, characters are less spaced than on svg rendering by browser.
Position looks corrects but you can see is never pixel perfect on rendering
polyline.class.js - Fixes polyline in svg rendering import, skipoffset come just from FromElement method.
polygon.class.js - Fixes position in polygon from svg import skipoffset come just fromElement method
path.class.js - Fix path position in svg import with transformMatrix
parser.js - Viewbox fix.
Viewbox generates a transform matrix of translating and scaling that should be applied to all elements.
We do this creating a element with a transformMatrix that then descend on all elements using the already existing parsing functions.

Tested and uploaded here 
http://www.deltalink.it/andreab/fabric/a.html

to compare fabric 1.4.8 with similar method 
http://www.deltalink.it/andreab/fabric/b.html

Object imported are not centered or top-lefted they go naturally on 0,0 because position are corrected.

![image](https://cloud.githubusercontent.com/assets/1194048/3626835/69f9f0ee-0e82-11e4-863b-deb4ae2d1dec.png)

Some visual effects of svg currently not rendering good in svg import test:

![image](https://cloud.githubusercontent.com/assets/1194048/3626863/bee648e6-0e82-11e4-9c31-23b966f32773.png)

![image](https://cloud.githubusercontent.com/assets/1194048/3626865/c8b4e7f6-0e82-11e4-9754-ed93bc3798ff.png)

![image](https://cloud.githubusercontent.com/assets/1194048/3626877/ece9731c-0e82-11e4-868f-7176cc9b996e.png)