Khan/khan-exercises — pull request #13238 by ben-smith (2012-02-07 10:28:14+00:00)
Title: Fixes graphical issue in Fractions cut and copy

Added a single line to call clear on Raphael paper objects when they
update. This prevents graphical issues in IE9 and prevents build-up of svg paths in the HTML document in all browsers as the user interacts with the rectangular slicing.