Implement mp_parse_node_free; print properly repr(string).
diff --git a/py/builtinimport.c b/py/builtinimport.c
index 3cfd64e..35e7dcb 100644
--- a/py/builtinimport.c
+++ b/py/builtinimport.c
@@ -29,9 +29,7 @@
     }
     */
 
-    uint mod_name_l;
-    const byte *mod_name_s = mp_obj_str_get_data(args[0], &mod_name_l);
-    qstr mod_name = qstr_from_strn((const char*)mod_name_s, mod_name_l);
+    qstr mod_name = mp_obj_str_get_qstr(args[0]);
 
     mp_obj_t loaded = mp_obj_module_get(mod_name);
     if (loaded != MP_OBJ_NULL) {
@@ -44,6 +42,7 @@
         // TODO handle lexer error correctly
         return mp_const_none;
     }
+    qstr source_name = mp_lexer_source_name(lex);
 
     // create a new module object
     mp_obj_t module_obj = mp_obj_new_module(mod_name);
@@ -60,7 +59,6 @@
     qstr parse_exc_id;
     const char *parse_exc_msg;
     mp_parse_node_t pn = mp_parse(lex, MP_PARSE_FILE_INPUT, &parse_exc_id, &parse_exc_msg);
-    qstr source_name = mp_lexer_source_name(lex);
     mp_lexer_free(lex);
 
     if (pn == MP_PARSE_NODE_NULL) {
@@ -72,6 +70,7 @@
 
     // compile the imported script
     mp_obj_t module_fun = mp_compile(pn, source_name, false);
+    mp_parse_node_free(pn);
 
     if (module_fun == mp_const_none) {
         // TODO handle compile error correctly