fix setViewBox bugs.

call transform method with '...' param make different result Chrome, IE8.
problem all gone when send empty string parameter.

i think this change is make no different SVG/VML Render.

######sample code
```javascript
var paper = Raphael('canv', 640, 480);

paper.rect(5, 5, 50, 50).attr({
    fill: 'red',
    stroke: 'none'
});

document.getElementById('zoomIn').onclick = function() {
    paper.setViewBox(0, 0, 1024, 768);
};

document.getElementById('zoomOut').onclick = function() {
    paper.setViewBox(0, 0, 320, 240);
};
```

in Chrome
![setviewbox_chrome](https://cloud.githubusercontent.com/assets/1061205/4387964/8c59472e-43e4-11e4-84cf-a5a18b1371b4.gif)


in IE8 (Buggy)
![setviewbox_ie8](https://cloud.githubusercontent.com/assets/1061205/4387967/977428ae-43e4-11e4-8d8f-5cb64947cae8.gif)