TinyMCE 3.5.8 update; some fixes

* Update TinyMCE to 3.58
* Fix [code] blocks to preserve HTML tags (I think we want this, if not I'll remove it)
* Fix bug where two `<img>` tags would be caught in one regular expression
* TinyMCE (still) has a bug where if forced_root_block is set to '', then the cursor acts weird when you try to use Code or sometimes even Blockquote. I've tried to work around it by setting forced_root_block to 'div' and then stripping the divs out with the BBcode parser