tests: conditionalize extension tests for extra extensions If extra extensions are loaded (e.g. via --extra-config-opt), the tests conditionalized in this commit fail in ways that are dependent on the extensions that are loaded. So let's skip them when that scenario is present. This drops the number of failures for the simplestorerepo.py extension to 4. Differential Revision: https://phab.mercurial-scm.org/D4285

commit: try hard to reuse p1 manifest if nothing changed This is all for commit reproducibility on "hg convert". With this change, p1 manifest is reused if ctx.files() *to be committed* is empty, and if new manifest entry is identical to p1. This is important property for "hg convert" since memctx.files() built from a convert source may be either a) more narrowed thanks to a committed ctx.files() which provides more accurate status, or b) containing redundant files because of sloppy filtering on e.g. octopus merge.