issue6528: add a config option to control the fixing on the fly This will allow people who know to be safe to avoid any performance overhead (and other potential issue). Differential Revision: https://phab.mercurial-scm.org/D11271

issue6528: also filter delta on the fly when applying a changegroup This ensure that corrupted clone does not spread corruption to "fixed" version. This might come at a performance cost, we will had a config option to control this behavior in the next changesets. Differential Revision: https://phab.mercurial-scm.org/D11270

filelog: open the writing context a bit earlier in `addgroup` This is a small change made ahead of the next patch for clarification. Differential Revision: https://phab.mercurial-scm.org/D11269

issue6528: implement _is_revision_affected_fast using callback The delta comming from a bundle/stream does not exists in the revlog yet, so we will need other way to retrieve the same information. To prepare for this we split the function to use callbacks in the core logic. Differential Revision: https://phab.mercurial-scm.org/D11268