Using die() for some more error messages.

tests/t1020-addtolistfile.sh

@@ -13,6 +13,7 @@ commands work, including support for filtering.
 test_todo_session 'nonexistant file' <<EOF
 >>> todo.sh addto garden.txt notice the daisies
 TODO: Destination file $HOME/garden.txt does not exist.
+=== 1
 EOF
 
 touch "$HOME/garden.txt"

tests/t1800-del.sh

@@ -139,7 +139,7 @@ EOF
 test_todo_session 'del nonexistant TERM' <<EOF
 >>> todo.sh del 1 dung
 1: (B) smell the uppercase Roses +flowers @outside
-'dung' not found; no removal done.
+TODO: 'dung' not found; no removal done.
 === 1
 
 >>> todo.sh -p list