Fix javascript error in IE7/IE8 on Windows XP.

On IE7/IE8, the DOM should not be changed before the domReady event has
been fired.

More information:
http://stackoverflow.com/questions/13731921/script-error-unable-to-modify-the-parent-container

Essentially the same fix in another module:
https://github.com/collective/collective.z3cform.datetimewidget/commit/92415cd0faf9440ac759b56