Cache fixes:

* We now cache negative lookups; clear them in Memcached_DataObject->insert()
* Mark file.url as a unique key in statusnet.ini so its negative lookups are cleared properly (first save of a notice with a new URL was failing due to double-insert)
* Now using serialization for default in-process cache instead of just saving objects; avoids potential corruption if you save an object to cache, change the original object, then fetch the same key from cache again

classes/Memcached_DataObject.php

@@ -142,6 +142,7 @@ class Memcached_DataObject extends DB_DataObject
 
     function insert()
     {
+        $this->decache(); // in case of cached negative lookups
         $result = parent::insert();
         return $result;
     }

classes/statusnet.ini

@@ -92,6 +92,7 @@ modified = 384
 
 [file__keys]
 id = N
+url = U
 
 [file_oembed]
 file_id = 129

lib/cache.php

@@ -120,7 +120,7 @@ class Cache
 
         if (Event::handle('StartCacheGet', array(&$key, &$value))) {
             if (array_key_exists($key, $this->_items)) {
-                $value = $this->_items[$key];
+                $value = unserialize($this->_items[$key]);
             }
             Event::handle('EndCacheGet', array($key, &$value));
         }
@@ -146,7 +146,7 @@ class Cache
         if (Event::handle('StartCacheSet', array(&$key, &$value, &$flag,
                                                  &$expiry, &$success))) {
 
-            $this->_items[$key] = $value;
+            $this->_items[$key] = serialize($value);
 
             $success = true;