Unable to add/remove row/columns in IE8

Clicking any of the add/remove buttons for rows/columns appears to be busted in IE8.
I steal [python's](http://legacy.python.org/dev/peps/pep-0008/#designing-for-inheritance) convention of using `_` to delimit a method or attribute as private. Once we hit 1.0, we are committed to not breaking non-private things that plugin authors might rely on.