[ticket/12211] Do not run attachment file names twice through htmlspecialchars

Upload filenames are already processed via htmlspecialchars in the
type_cast_helper of the new request class. There is no need to run it through
htmlspecialchars() again in the filespec class.

PHPBB3-12211
Merge remote-tracking branch 'marc/ticket/12211' into develop-ascraeus

* marc/ticket/12211:
  [ticket/12211] Do not run attachment file names twice through htmlspecialchars
[ticket/12395] Check for posts in the middle of the page

PHPBB3-12395
Merge remote-tracking branch 'nickvergessen/ticket/12395' into develop-ascraeus

* nickvergessen/ticket/12395:
  [ticket/12395] Check for posts in the middle of the page
[ticket/10737] Adding username suggestions in "Find a member" using AJAX

PHPBB3-10737
[ticket/10737] Improvements over last commit

PHPBB3-10737
[ticket/10737] Code fixes in AJAX search feature

PHPBB3-10737
[ticket/10737] Using JQuery events and JSON response.

PHPBB3-10737
[ticket/10737] Removing unnecessary/obsolete code.

PHPBB3-10737
[ticket/10737] Avoid hard-coding table row and use case-insensitive search.

PHPBB3-10737
[ticket/10737] Removing obsolete code.

PHPBB3-10737
[ticket/10737] Using UTF-8 aware alternatives in PHP code.

PHPBB3-10737
[ticket/10737] Adding delayed keyup and removing target_blank.

PHPBB3-10737
[ticket/10737] Use dropdown for search results container.

PHPBB3-10737
[ticket/10737] Clean up memberlist.php.

PHPBB3-10737
[ticket/10737] Add a more generic live search implementation.

PHPBB3-10737
[ticket/10737] Drop subsilver2 changes.

PHPBB3-10737
[ticket/10737] Set the username as the input value instead of redirecting.

PHPBB3-10737
[ticket/10737] Load core.js and ajax.js in simple_footer.html.

PHPBB3-10737
[ticket/10737] Add loading indicator and alert box code to simple_footer.html.

PHPBB3-10737