Mail cloak broken when text contains non-ascii

Add in an article a mail of type:
```
<p><a href="mailto:admin@mysite.com">été</a></p>
```
The cloaking will not work.
Patch and test again.

Same issue in 2.5. This had been solved a long time ago in 1.5:
http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=11578
See: https://github.com/joomla/joomla-cms/pull/3718#issuecomment-49133477

Remains to solve the case when an address is entered as
```
<p>ete@mysite.com</p>
```
which was working before https://github.com/joomla/joomla-cms/pull/3718