bug in aight's shim for Element.prototype.textContent results in "Unspecified error."

I've traced the issue to [element-properties.js](/shawnbot/aight/blob/master/js/element-properties.js).

Here's the gist (sorry, neither jsbin nor jsFiddle support IE8 anymore):

https://gist.github.com/usmonster/9349332

~~Notice I load aight *after* jQuery. (Loading before causes other issues... see, e.g., #24.)
Note also that this could affect libraries or JS other than jQuery.~~