IE problem introduced in SVN 621

In SVN 621, I changed the TeX preprocessor to fix a problem with Firefox and empty text nodes when they appear in pre-formatted text (it caused unwanted blank lines to appear). Apparently, IE removes these nodes automatically, so the fix causes an error when it tries to remove them again (the parentNode is null).

The fix is to add a check for null parentNode in tex2jax.js line 213, changing

if (search.open.nodeValue === "") 
  {search.open.parentNode.removeChild(search.open)}

to

if (search.open.nodeValue === "" && search.open.parentNode)
  {search.open.parentNode.removeChild(search.open)}

This is in my fork of MathJax. Sean, can you review this so that I can make the change? Thanks.

Davide