-Revert (r26736): reverse_iterators are invalidated when the element next to them is erased (not the element they are pointing to), which makes them unsuitable for ScriptList.

git-svn-id: http://svn.openttd.org/trunk@26741 6aa0318a-3be1-0310-93fa-89fd2396df07
-Doc: Why reverse_iterator is unsuitable for ScriptList iterators

git-svn-id: http://svn.openttd.org/trunk@26742 6aa0318a-3be1-0310-93fa-89fd2396df07
-Codechange: Simplify ScriptList iterators.

git-svn-id: http://svn.openttd.org/trunk@26743 6aa0318a-3be1-0310-93fa-89fd2396df07
-Fix [FS6085-ish]: ScriptListSorterItemDescending::FindNext failed to detect the end.

git-svn-id: http://svn.openttd.org/trunk@26744 6aa0318a-3be1-0310-93fa-89fd2396df07