Convert a bunch of constant strings in C to unicode.
diff --git a/Objects/setobject.c b/Objects/setobject.c
index 2cc1743..7ff27b1 100644
--- a/Objects/setobject.c
+++ b/Objects/setobject.c
@@ -966,7 +966,7 @@
 	register PySetObject *so = NULL;
 
 	if (dummy == NULL) { /* Auto-initialize dummy */
-		dummy = PyString_FromString("<dummy key>");
+		dummy = PyUnicode_FromString("<dummy key>");
 		if (dummy == NULL)
 			return NULL;
 	}