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.

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.

merge with stable

py3: convert return values of inspect.getabsfile() to bytes It's weird that python docs for inspect does not mention getabsfile(). Differential Revision: https://phab.mercurial-scm.org/D6033

py3: add two new passing tests found by buildbot Differential Revision: https://phab.mercurial-scm.org/D6032

py3: make contrib/debugshell.py work with Python 3 I changed default mercurial installation of my personal laptop to one installed with python 3.7. debugshell is one of the extension which I have enabled and it was failing. This patch makes debugshell works with Python 3. I found that chg does not work with python 3. Differential Revision: https://phab.mercurial-scm.org/D6031

absorb: let scmutil.cleanupnodes() take care of setting phase Differential Revision: https://phab.mercurial-scm.org/D6036

absorb: use scmutil.cleanupnodes() also when obsmarkers are disabled A side-effect of this is the new warning in the test case, but the warning is valid, so I don't think that's a problem. Differential Revision: https://phab.mercurial-scm.org/D6035