Fixed an unknown issue on a ProcessWire module. This gist is just temporary.

gistfile1.php

<?php
/**
*
* Multisite module for Processwire
* (C) 2012 Antti Peisa, Avoine Oy
*
* ProcessWire 2.x
* Copyright (C) 2010 by Ryan Cramer
* Licensed under GNU/GPL v2, see LICENSE.TXT
*
* http://www.processwire.com
* http://www.ryancramer.com
*
*/
class Multisite extends WireData implements Module, ConfigurableModule {
public static function getModuleInfo() {
  return array(
   'title' => 'Multisite',
   'version' => 001,
   'summary' => 'Allows multiple sites with different domains run from single PW-site and database.',
   'singular' => true,
   'autoload' => true,
   );
}
public function init() {
  $this->subdomainsArray = explode("\n", strtolower($this->subdomains));
  $this->it = (isset($_GET['it'])) ? ltrim($_GET['it'], '/') : '';
  foreach($this->subdomainsArray as $subdomain) {
   $subdomain = trim($subdomain);
   $config = wire('config');
   $httpHost = strtolower(wire('config')->httpHost);
   if(strpos($httpHost, $subdomain) !== false) {
        $this->subdomain = $subdomain;
        // change path like /about/contact/ to /campaign.com/about/contact/
        @$_GET['it'] = "/{$subdomain}/" . ltrim($_GET['it'], '/');
        // hook for path method to make path() and url() methods context aware
        $this->addHookAfter('Page::path', $this, 'modifyPath');
        break;
   }
  }
}
public function ready() {
  // if $this->subdomain was valid in init(), then no need to do more here.
  if($this->subdomain) return;
  $this->subdomain = $this->page->rootParent->name;
  // if rootParent->name isn't a subdomain, then no need to continue
  if(!in_array($this->subdomain, $this->subdomainsArray)) return;
  // if subdomain is visible on url, we might wanna redirect
  if(strpos($this->it, $this->subdomain) === 0 && !$this->page->editable()) {
   $http = ($this->config->https) ? "https://" : "http://";
   $url = $http . $this->subdomain;
   $url .= str_replace("/{$this->subdomain}/", '/', $this->page->url);
   $this->session->redirect($url);
  }
}
public function modifyPath($event) {
  $event->return = str_replace("{$this->subdomain}/", '', $event->return);
}
static public function getModuleConfigInputfields(array $data) {
  $fields = new InputfieldWrapper();
  $modules = wire('modules');
  $field = $modules->get("InputfieldTextarea");
  $field->name = "subdomains";
  $field->label = "Other sites running from same install";
  $field->description = "Add each domain for their own line. Don't add http or https, just simple domain like: www.example.com tai campaign.example.com";
  $field->notes = "IMPORTANT: create homepage for each of these domains right on the root. Name should be exactly same as the domain you use here.";
  $field->attr('value', $data['subdomains']);
  $fields->add($field);
  return $fields;
}
}