ENH: Allow configuring null data files and then don't create them.

Request from exatto (http://article.gmane.org/gmane.comp.diary.todotxt/4699), who doesn't want to use done.txt and report.txt.

Also consider character devices (-c; /dev/null is one) in the file existence checks so that no empty file is then created.

tests/t2200-no-done-report-files.sh

@@ -0,0 +1,49 @@
+#!/bin/bash
+#
+
+test_description='todo.sh configuration with a sole todo.txt data file.
+
+This test covers turning off done.txt and report.txt, and
+checks that no such empty files are created.
+'
+. ./test-lib.sh
+
+cat > test.cfg << EOF
+export TODO_DIR=.
+export TODO_FILE="\$TODO_DIR/todo.txt"
+export DONE_FILE=/dev/null
+export REPORT_FILE=/dev/null
+export TMP_FILE="\$TODO_DIR/todo.tmp"
+touch used_config
+EOF
+
+test_todo_session 'invoke todo.sh' <<EOF
+>>> todo.sh -d test.cfg add notice the daisies
+1 notice the daisies
+TODO: 1 added.
+EOF
+
+test_expect_success 'the todo file has been created' '[ -e todo.txt ]'
+test_expect_success 'no done file has been created' '[ ! -e done.txt ]'
+test_expect_success 'no report file has been created' '[ ! -e report.txt ]'
+
+test_todo_session 'perform archive' <<EOF
+>>> todo.sh -A -d test.cfg do 1
+1 x 2009-02-13 notice the daisies
+TODO: 1 marked as done.
+x 2009-02-13 notice the daisies
+TODO: ./todo.txt archived.
+EOF
+
+test_expect_success 'no done file has been created by the archiving' '[ ! -e done.txt ]'
+
+test_todo_session 'perform report' <<EOF
+>>> todo.sh -d test.cfg report
+TODO: ./todo.txt archived.
+2009-02-13T04:40:00 0 0
+TODO: Report file updated.
+EOF
+
+test_expect_success 'no report file has been created by the reporting' '[ ! -e report.txt ]'
+
+test_done