fix for 0004258: Username used instead of real name (in history for
monitor/unmonitor)

• switch user_get_name for user_get_field('username')

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@3002 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9