Network policy is to answer in answers rather than in comments. You're not supposed to actually answer the question with a comment.
We do tend to tolerate partial answers in comments on CV, especially when they're intended as hints/guidance -- somewhat more so than many other SE sites and likely a good deal more so than originally intended. [Some SE sites are very strict on this, straight out deleting any comment that remotely looks like even a partial answer.]
Even though we're a little more tolerant than the average of comments that would be partial answers here (and sometimes with good reason, I think), if a full answer (or a nearly-complete one) appears in comments, it should instead be posted as an answer.
We have enough problems with unanswered questions as it is. Speaking for myself, I think we should encourage the turning of comment-answers into proper answers by any available means.
[math.SE is a bit nearer to us in tolerating part-answer/hinty comments, though there's a tendency there to encourage conversion to an answer when it comes close to an answer... and they don't have as much of an issue with low answer rates as we do.]
If the poster of an answer-as-a-comment does not make it an answer within a pretty short time (a couple of hours seems plenty to me), I would encourage anyone who sees it to simply do so themselves.
Appropriate credit should be given if you post an answer that relies on a comment in any substantive way, though it's possible that two people would give very similar responses without the poster of an answer even having read the comment-answer (so we should try not be overly critical if credit were occasionally seemingly omitted; comment-posters can hardly complain when that happens).
However, if you do post such an answer, responsibility for its content is then yours, not that of the commenter.
If you don't want the responsibility and/or the reward (as meagre as it usually is), there's always the possibility to make the answer community wiki (if you have the privilege, you can simply click in the box under the bottom right of the edit window before you click "post answer" -- and if you don't have the privilege you can always flag and ask a moderator to do it)