storage: introduce a `revlog.reuse-external-delta` config
This option goes a bit further and provides a way to get the same behavior as the
`re-delta-all` optimisation from `hg debugupgraderepo`.
The effect of the option is a bit hard to test as we do not have multiple diff
algorithm at hand. However, we at least make sure the code path run.
Mercurial
=========
Mercurial is a fast, easy to use, distributed revision control tool
for software developers.
Basic install::
$ make # see install targets
$ make install # do a system-wide install
$ hg debuginstall # sanity-check setup
$ hg # see help
Running without installing::
$ make local # build for inplace usage
$ ./hg --version # should show the latest version
See https://mercurial-scm.org/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.