test-merge-tools: fix flaky test by avoiding debugsetparents debugsetparents is a debug command and does not provide the same guarantees as non-debug commands do. In particular, when the user sets a different parent, any clean files will remain clean in the dirstate even though the new parent might have a different version of the file (so it should appear modified compared to the new parent). Let's instead achieve the same effect by updating to the new parent and reverting the contents back to what they were. This fix can be tested by passing '--config debug.dirstate.delaywrite=2' to the 'hg update' command in the beforemerge().

revlog: in addgroup, reject ill-formed deltas based on censored nodes To ensure interoperability when clones disagree about which file nodes are censored, a restriction is made on deltas based on censored nodes. Any such delta must replace the full text of the base in a single patch. If the recipient of a delta considers the base to be censored and the delta is not in the expected form, the recipient must reject it, as it can't know if the source has also censored the base. For background and broader design of the censorship feature, see: http://mercurial.selenic.com/wiki/CensorPlan

mdiff: add helper for making deltas which replace the full text of a revision This helper will be used initially for censor-aware delta generation. Deltas which replace the full contents of the base revision are guaranteed to apply correctly regardless of whether the delta recipient has censored the base. For background and broader design of the censorship feature, see: http://mercurial.selenic.com/wiki/CensorPlan