When splitting, avoid making a copy of the string if the split doesn't find
anything (issue 1538).
diff --git a/Misc/NEWS b/Misc/NEWS
index efcb6c0..4db5c3d 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,9 @@
 Core and builtins
 -----------------
 
+- Issue #1538: Avoid copying string in split/rsplit if the split
+  char is not found.
+
 - Issue #1553: An erroneous __length_hint__ can make list() raise a
   SystemError.