Adjust so failing with ENOTEMPTY is ok, too.

That happens with Linux/tmpfs.

tests/mv/dir2dir

@@ -35,8 +35,11 @@ fail=0
 # diagnostic about moving one directory to a subdirectory of itself.
 mv b/t a 2> out && fail=1
 
+# Accept either EEXIST or ENOTEMPTY.
+sed 's/: File exists/: Directory not empty/'<out>o1;mv o1 out
+
 cat <<\EOF > exp || fail=1
-mv: cannot move `b/t' to `a/t': File exists
+mv: cannot move `b/t' to `a/t': Directory not empty
 EOF
 
 cmp out exp || fail=1