fix(?) for issue 2222 - untick removes too little XP,GP

This is a proposed fix for issue 2222 ("unticking a todo with a checklist removes much less XP and GP than it should") BUT I HAVE NOT TESTED THIS (I don't have a local install yet - sorry). Please see my comments at the end of that issue. Note that I don't know why "if direction is 'up'" was originally included - there might have been (and still be) a good reason for it.
Merge pull request #73 from Alys/patch-2

fix(?) for issue 2222 - untick removes too little XP,GP