The following pages now have a <title> that can be set in localizations:
* /user/USER_DOES_NOT_EXIST
* /user/USER_DOES_NOT_EXIST/diary
* /user/USER_DOES_NOT_EXIST/traces
* /message/*/ID_DOES_NOT_EXIST
In addition I've cleaned up the i18n message keys of all the
''no_such_user.rhtml'' pages involved. They now all use
title/heading/body for the <title>, <h2> and <p> respectively. And the
message key {{user}} instead of {{name}}.
