prevent more than one usercard shown at a time

lib/persona.js

@@ -175,6 +175,8 @@ $(document).ready(function() {
 			index = avatar.parents('[data-index]').attr('data-index'),
 			data = (ajaxify.data.topics || ajaxify.data.posts)[index].user;
 
+		$('.persona-usercard').remove();
+
 		socket.emit('user.isFollowing', {uid: data.uid}, function(err, isFollowing) {
 			app.parseAndTranslate('modules/usercard', data, function(html) {
 				var card = $(html);