Pointed out by Chris Gaukroger.

as they are probably very rarely intresting to the "common people" anyway.

doing proxy authentication.

content-type after a transfer.

previous difference was not clear nor documented properly). They can now both
be used interchangeably, but we prefer UPLOAD to PUT since it is a more
generic term.

might be done differently in the future.

function fails and it returns NULL

we can compare if non-NULL elsewhere