Move content-type setting to controller plugin.

This tries harder to avoid any duplicate setting of the content-type
header, which breaks fastcgi setups.

application/libraries/Omeka/Application/Resource/Frontcontroller.php

@@ -52,6 +52,9 @@ public function init()
             $front->registerPlugin(
                 new Omeka_Controller_Plugin_Ssl((string)$sslConfig, $redirector, $auth));
         }
+
+        // Add a default content-type fallback.
+        $front->registerPlugin(new Omeka_Controller_Plugin_DefaultContentType);
 
         return $front;
     }

application/libraries/Omeka/Controller/AbstractActionController.php

@@ -50,7 +50,6 @@ public function __construct(Zend_Controller_Request_Abstract $request,
                                 array $invokeArgs = array()
     ) {
         parent::__construct($request, $response, $invokeArgs);
-        $response->setHeader('Content-Type', 'text/html; charset=utf-8', true);
         $this->_setActionContexts();
     }
 

application/libraries/Omeka/Controller/Plugin/DefaultContentType.php

@@ -0,0 +1,38 @@
+<?php
+/**
+ * Omeka
+ * 
+ * @copyright Copyright 2007-2012 Roy Rosenzweig Center for History and New Media
+ * @license http://www.gnu.org/licenses/gpl-3.0.txt GNU GPLv3
+ */
+
+/**
+ * This controller plugin sets the default Content-Type header when one hasn't
+ * been set at the end of the controller processing.
+ *
+ * This has to be done here because Zend allows header duplication, the
+ * output contexts don't overwrite headers of the same name, and some servers
+ * (FastCGI) choke when they see two Content-Type headers.
+ */
+class Omeka_Controller_Plugin_DefaultContentType extends Zend_Controller_Plugin_Abstract
+{
+    /**
+     * Add a default Content-Type to the response if none is already set.
+     */
+    public function dispatchLoopShutdown()
+    {
+        $response = $this->getResponse();
+
+        $typeAlreadySet = false;
+        foreach ($response->getHeaders() as $header) {
+            if ($header['name'] == 'Content-Type') {
+                $typeAlreadySet = true;
+                break;
+            }
+        }
+
+        if (!$typeAlreadySet) {
+            $response->setHeader('Content-Type', 'text/html; charset=utf-8');
+        }
+    }
+}