Chosen does not get rendered when using toggling visiblity of parent

Currently I was using tabs with jQuery, and a chosen-box was placed in a tab.
Unfortunately when the chosen-box, if not placed in the initial visible tab, gets visible (by changing the tab), the width is fukced up.

Therefore I've introduced a new init-parameter (options.width) which could be used eg:

```javascript
$box.chosen({
	'width': '80%'
});
```

The widths of the search-container and search-field get set on-demand (on showing the container)