PATCH method and is_conflict

[benjamin-bergia]

After working on some rest handlers for PATCH requests, I noticed that only PUT requests go through the is_conflict function and as such can return a 409.

I wasn't sure about this but, apparently, the rfc
do mention 409 and 412 as possible return codes in case of conflict.

[essen]

Some conflicts will happen when you do the actual modification and it's up to you to return a 409 in that case, but I agree that some conflicts may be detected in is_conflict the same way as for PUT and we should probably allow it.

[essen]

I would like to do this soon but I'm conflicted on whether this should be a 2.x change or a 3.0 change, since it'll change drastically how cowboy_rest executes when doing PATCH requests compared to the current code and documentation. But the RFC says the code and documentation is wrong, so maybe it should be treated as a bug. I dunno.