storage: introduce a `revlog.reuse-external-delta-parent` config...
storage: introduce a `revlog.reuse-external-delta-parent` config
As pointed in c59987ab96b4, we had no simple way to get a client to not blindly
reuse the delta parent from a bundle. Instead one had to rely on a side effect
of the deprecated `format.generaldelta` configuration.
We introduce an explicit `revlog.reuse-external-delta-parent` configuration
option (default to True) to control this behavior. If the option is not set,
`format.generaldelta` still control this behavior.
To test the new option, we convert a couple of place where `generaldelta` have
been used for its side effects.
