Recurring Tasks

- Rewrote updateRecurrenceMask, which was hopelessly muddled after the
  TDB -> TDB2 change.
- Modified associated code.
- Improved signal to noise ratio in unit tests.

test/recur.until.t

@@ -48,7 +48,10 @@ like ($output, qr/^\s+3/ms, 'Found 3');
 like ($output, qr/^\s+4/ms, 'Found 4');
 like ($output, qr/^\s+5/ms, 'Found 5');
 
-qx{../src/task rc:recur.rc $_ do} for 1..5;
+qx{../src/task rc:recur.rc 2 do};
+qx{../src/task rc:recur.rc 3 do};
+qx{../src/task rc:recur.rc 4 do};
+qx{../src/task rc:recur.rc 5 do};
 $output = qx{../src/task rc:recur.rc list};
 like ($output, qr/and has been deleted/, 'Parent task deleted');