add test for issue433

tests/test-issue433

@@ -0,0 +1,10 b''
+#!/bin/sh
+# http://www.selenic.com/mercurial/bts/issue433
+
+hg init a
+cd a       
+echo a > a 
+hg commit -Ama 
+
+hg parents -r 0 doesnotexist
+true

tests/test-issue433.out

@@ -0,0 +1,2 b''
+adding a
+abort: 'doesnotexist' not found in manifest!