The path for custom avatars is stored already. So I would use this approach instead of hard coding the path.
Code:
<img src="'.$vbulletin->options['avatarpath'].'/avatar'.$featureduser[userid].'_'.$featureduser[avatarrevision].'.gif" alt="'.$featureduser[username].'" width="125" height="125">
You do not need to include either function file. You are not using any functions from them -- at least in the code you showed us.