patch 7.4.1051
Problem:    Segfault when unletting "count".
Solution:   Check for readonly and locked first. (Dominique Pelle)
            Add a test.
diff --git a/src/testdir/test_alot.vim b/src/testdir/test_alot.vim
index 9800afc..413e71b 100644
--- a/src/testdir/test_alot.vim
+++ b/src/testdir/test_alot.vim
@@ -8,3 +8,4 @@
 source test_set.vim
 source test_sort.vim
 source test_undolevels.vim
+source test_unlet.vim