function _fnConvertToWidth ( width, parent )
	{
		if ( ! width ) {
			return 0;
		}
	
		var n = $('<div/>')
			.css( 'width', _fnStringToCss( width ) )
			.appendTo( parent || document.body );
	
		var val = n[0].offsetWidth;
		n.remove();
	
		return val;
	}
Convert a CSS unit width to pixels (e.g. 2em)
 @param {string} width width to be converted
 @param {node} parent parent to get the with for (required for relative widths) - optional
 @returns {int} width in pixels
 @memberof DataTable#oApi