Core and Default plugins separated, now loads on install

_flow_ reported on IRC that install.php had stopped working. This was
because default plugins had been put into two separate lists, and the
list with AuthCrypt was never loaded when performing an installation.

Core plugins cannot be disabled.

I also removed the Memcache autodetection thing since it should be
solved in a more elegant manner.

lib/statusnet.php

@@ -181,6 +181,11 @@ class StatusNet
      */
     protected static function initPlugins()
     {
+        // Load core plugins
+        foreach (common_config('plugins', 'core') as $name => $params) {
+            call_user_func('addPlugin', $name, $params);
+        }
+
         // Load default plugins
         foreach (common_config('plugins', 'default') as $name => $params) {
             $key = 'disable-' . $name;