[FIX] Web: OpenerpFramework: replaceElement on multiple roots nodeset

jquery's `replaceWith` function behaves differently between 1.8 and 1.9.
This function is used by `renderElement` of the Odoo widget API and, when
called on a template with multiple root nodes, will fail to replace the
whole original nodeset by the new but instead will replace every node
by the new nodeset.

Sample:
1) Suppose a DOM containing
    <div>1</div>
    <div>2</div>
and a jquery nodeset [<div>1</div>, <div>2</div>] referring to the
previous DOM part in a var named $oldel.;
2) suppose another jquery nodeset [<div>3</div>, <div>4</div>] in $el;

$oldel.replaceWith($el) will result in
"3434" in jquery 1.9.1
"34" in jquery 1.8.3

This issue particulary concerns us when the dom of a widget is not wrapped
into single tag and when re-calling renderElement (triggering renderElement).

The fix is to wrap the element to be replaced ($oldel in the example) behind
a div before calling replaceWith.