heartcode/CanvasLoader — pull request #23 by allmywant (2013-08-27 14:02:13+00:00)
Title: fixed "null !== undefined" issue

it was "if (document.getElementById(pId) !== undefined)", it's not
correct,
if lookup faild, e.g. we want set the parent element = document.body,i
pass pId=null or '' document.getElementById(pId)=null,
(null !== undefined)==true, thus this.mum == null.