MDL-28364 handle question formats that support multiple file types

question/format.php

@@ -102,6 +102,20 @@ class qformat_default {
     public function export_file_extension() {
         return '.txt';
     }
+    
+    /**
+     * Check if the given file is capable of being imported by this plugin.
+     *
+     * Note that expensive or detailed integrity checks on the file should
+     * not be performed by this method. Simple file type or magic-number tests
+     * would be suitable.
+     *
+     * @param stored_file $file the file to check 
+     * @return bool whether this plugin can import the file
+     */
+    public function can_import_file($file) {
+        return ($file->get_mimetype() == $this->mime_type());
+    }
 
     // Accessor methods