`load` throws a warning since a change in R serialization format that came with v3.5/3.6

[reumle]

• first mentioned in the (closed) issue load not working #75

As @alyst clarifies in that issue, load works with the new format, (it certainly does in my experience) but throws a warning. Some more analysis of the new format is needed, in order to fully manage it.

See also issue #74

Help welcome!