Fix 8353: Handling accentuated tags.

This is done by changing the whitelisting method to a blacklist
Also added proper form submission when some tags are invalid

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@5437 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9