Fix for https://en.wikipedia.org/wiki/Wikipedia_talk:AutoWikiBrowser/Bugs#Single_click_to_focus_the_edit_box_to_a_line_-_no_longer_works_with_SVN9282
Determine whether Microsoft.Mshtml can be loaded, not just if it's an available assembly

git-svn-id: svn://svn.code.sf.net/p/autowikibrowser/code@9305 5227b50d-9349-4574-b055-4b0a7525e11c