Add local directory for plugins, themes, etc.

Added a local directory for locally-installed software. This is where
you should put any code you write, themes, plugins, etc. so they don't
get stomped by upgrades.

classes/User.php

@@ -121,7 +121,8 @@ class User extends Memcached_DataObject
         static $blacklist = array('rss', 'xrds', 'doc', 'main',
                                   'settings', 'notice', 'user',
                                   'search', 'avatar', 'tag', 'tags',
-                                  'api', 'message', 'group', 'groups');
+                                  'api', 'message', 'group', 'groups',
+                                  'local');
         $merged = array_merge($blacklist, common_config('nickname', 'blacklist'));
         return !in_array($nickname, $merged);
     }