Rework server_add. It's smaller and leaner now, storing the list of

files out in a separate model for scalability.  Removed the "pause"
functionality.

- Server_Add_Controller extends Admin_Controller so that we don't have
  to check for admin every time.
- Task completion time now factors in the time it takes to walk the
  arbitrarily deep trees
- Moved checkbox management entirely into JS using jQuery
- Simplified the JS considerably

modules/server_add/helpers/server_add.php

@@ -31,4 +31,19 @@ class server_add_Core {
       site_status::clear("server_add_configuration");
     }
   }
+
+  static function is_valid_path($path) {
+    if (!is_readable($path) || is_link($path)) {
+      return false;
+    }
+
+    $authorized_paths = unserialize(module::get_var("server_add", "authorized_paths"));
+    foreach (array_keys($authorized_paths) as $valid_path) {
+      if (strpos($path, $valid_path) === 0) {
+        return true;
+      }
+    }
+
+    return false;
+  }
 }