- fixed grouping error bug

- changed "group" operator to "groupref"
diff --git a/Modules/sre.h b/Modules/sre.h
index d4e93da..1c4bf68 100644
--- a/Modules/sre.h
+++ b/Modules/sre.h
@@ -46,6 +46,9 @@
     /* stack elements */
     SRE_CODE* pattern;
     void* ptr;
+    int mark;
+    void* mark0;
+    void* mark1;
 } SRE_STACK;
 
 /* FIXME: <fl> shouldn't be a constant, really... */