Clarify use of CURLOPT_RANGE on upload

[jay]

I did this

Christopher Head (@Hawk777) reported on the mailing list that CURLOPT_RANGE does not work properly for ranged PUTs. I replied saying PUT is only for complete replacement of a resource, not partial. He replied saying Amazon allows ranged PUTs (doc).

I expected the following

The documentation does not specify the behavior of CURLOPT_RANGE on upload, so we should clarify that and in doing so decide whether or not what was reported is a bug (I think it's not since it's against the RFC).

[bagder]

curl has an approach to resumed uploads with PUT, even though it isn't encouraged nor specified in the RFC. It has however existed for a long time so we don't want to break it either.

For example, test 1001 and 1041 verify the existing functionality.

[jay]

What do you think about changing the doc to link to caution against using CURLOPT_RANGE for PUT uploads?

See my final analysis at https://curl.haxx.se/mail/lib-2019-05/0012.html in the reply quoted and current

[bagder]

Absolutely, propose a change if you can come up with wording you think will help users!