Note when 13291 was introduced.

changes/bug13291-spawn-test-race-condition

@@ -1,4 +1,4 @@
   o Minor bugfixes:
     - Stop spawn test failures due to a race condition between the SIGCHLD
       handler updating the process status, and the test reading it.
-      Fixes bug 13291.
+      Fixes bug 13291; bugfix on 0.2.3.3-alpha.