If I'm not mistaken, that regex is checking for: =, /, " and ' 

I just tested with this:

    <a href="http://yahoo.com?var=http://yahoo.com">somelink</a>

And everything looks ok

I think the check for double-quotes is already covered in the existing unit test. I added a test for an existing anchor with single-quotes.

Like I said, I'm not a regex guru so I'm not absolutely sure :) But that seems to be doing it's job.