Do you really think the main motivation of contributing is to appear in the commit lists? I don't know if it's good to go in that direction, it might lead to people saying "look, I am part of the SFML development" or competitions between users concerning who contributes most, and a lot of trivial commits of which the merge overhead outweighs the feature -- in other words, people who only contribute for the sake of being visible in the commit list. Also, the repository owner shouldn't be under the pressure of applying a commit, because not doing so or implementing it himself (which would be faster in some cases) would appear as "unfair compared with others".
Of course, this is a pessimistic view, but eventually there will be a few people acting like this. In my opinion the motivation should generally be a different one, namely progress. If one really wants to push SFML (and even if it's only to have more features in one's own project), it's probably not too relevant who made which commit, especially not for smaller contributions. If it is (and I agree that notable contributions deserve to be credited), Laurent can still mention the name in a commit message, if that's easier to handle.
And I still find the points in my last post important, but of course it's up to Laurent how this is handled. But you can be sure, even if the SFML conventions are listed again and again, many people will not follow them exactly. In the case of smaller contributions, constantly rejecting commits and hinting to the mistakes takes up much more time than implementing things oneself. You see it in this forum, Laurent made a detailed thread explaining the forum rules and how to post a question meaningfully, yet every beginner ignores it. Sadly, sometimes even users with many posts seem not to care about it.
I'm not saying that people shouldn't be mentioned for their contributions -- but it does not justify a lot of additional effort, such as nitpicking trivial commits. So I would certainly not come up with something like a guideline that enforces the attribution of commits.