Fix 0003109: Error when adding protected users.

M core/user_api.php

• (user_set_field): Changed to allow setting the protected field for protected users.
• (user_create): Changed to create the user as unprotected, and protect it after
  setting the preferences.

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@2143 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9