fix for 0006084: default language for account registration

• don't push user language for signup message, there isn't one
  performance boost by pushing default language was broken
  if language = 'auto'

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@3773 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9