This implements the proposed spec clarification in
http://lists.w3.org/Archives/Public/www-style/2013Feb/0229.html which
makes us compatible with WebKit on the insertRule tests in this patch.
I confirmed that the test reports 7 failures without the patch, but
passes with the patch. (I'm a little disturbed by the way our
testharness.js integration elides runs of successive passes.)
L. David Baron