Add the ability to change a previously selected best answer by a new one

A small bug, It should be a elseif instead of else! New patch added.

Hi,
This new patch uses the code refactoring I introduced in https://drupal.org/node/1689720#comment-6267892 for the deselect feature.
So this new patch introduces 2 new perms, one for "own" and one for "any" question.
This patch works as a standalone, that is to say that it doesn't need any other patch to work. Hence you can test this new change link. The use case for this is for example when after a long time with inactivity someone post a new comment more accurate to answer a question which has already a best answer selected. In this case we don't need to deselect and then select a new one. This can be done in one step.
Please let me know, thanks,

Hi Jcisio,
Sorry for the delay, I'm just back from holidays. I've try your patch in #5 on my test website and, so far, it looks to work very well for all types of users.
So +1 for it.
BTW, your code refactoring is way better than mine ;-)
Best,

I found one minor issue. In question_answer.pages.inc line 24 we should have this:

$node->{$qtype[$node->type]['answer']}[0]['value'] = ($action == 'deselect') ? '' : $cid;

instead of this:

$node->{$qtype[$node->type]['answer']}[0]['value'] = ($action == 'deselect') ? 0 : $cid;

because when we are using duration the system check for an empty field and not a field filled with 0.

Yes this :

$node->{$qtype[$node->type]['answer']}[0]['value'] = ($action == 'deselect') ? NULL : $cid;

works well too.