Cosmetics: Add TODO: prefix to todo.txt do message on already done task.

The existing check didn't do much good, and one could deprioritize any normal task without notice. Instead, check that the task to be deprioritized actually has a priority and alert via "TODO: 42 is not prioritized." if that is not the case.

tests/t1500-do.sh

@@ -81,6 +81,6 @@ test_todo_session 'fail multiple do attempts' <<EOF
 TODO: 3 marked as done.
 
 >>> todo.sh -a do 3
-3 is already marked done
+TODO: 3 is already marked done.
 EOF
 test_done

tests/t1700-depri.sh

@@ -68,4 +68,30 @@ TODO: 2 deprioritized.
 TODO: 3 of 3 tasks shown
 EOF
 
+cat > todo.txt <<EOF
+(B) smell the uppercase Roses +flowers @outside
+(A) notice the sunflowers
+stop
+EOF
+test_todo_session 'depriority of unprioritized task' <<EOF
+>>> todo.sh -p list
+2 (A) notice the sunflowers
+1 (B) smell the uppercase Roses +flowers @outside
+3 stop
+--
+TODO: 3 of 3 tasks shown
+
+>>> todo.sh depri 3 2
+TODO: 3 is not prioritized.
+2 notice the sunflowers
+TODO: 2 deprioritized.
+
+>>> todo.sh -p list
+1 (B) smell the uppercase Roses +flowers @outside
+2 notice the sunflowers
+3 stop
+--
+TODO: 3 of 3 tasks shown
+EOF
+
 test_done

todo.sh

@@ -921,10 +921,7 @@ case $action in
 	todo=$(sed "$item!d" "$TODO_FILE")
 	[ -z "$todo" ] && die "TODO: No task $item."
 
-	sed -e $item"s/^(.) //" "$TODO_FILE" > /dev/null 2>&1
+	if sed "$item!d" "$TODO_FILE" | grep "^(.) " > /dev/null; then
-
-	if [ "$?" -eq 0 ]; then
-	    #it's all good, continue
 	    sed -i.bak -e $item"s/^(.) //" "$TODO_FILE"
 	    if [ $TODOTXT_VERBOSE -gt 0 ]; then
 		NEWTODO=$(sed "$item!d" "$TODO_FILE")
@@ -932,7 +929,7 @@ case $action in
 		echo "TODO: $item deprioritized."
 	    fi
 	else
-	    die "$errmsg"
+	    echo "TODO: $item is not prioritized."
 	fi
     done
     ;;
@@ -964,7 +961,7 @@ case $action in
                 echo "TODO: $item marked as done."
 	    fi
         else
-            echo "$item is already marked done"
+            echo "TODO: $item is already marked done."
         fi
     done