rust: lower compile error on non-linux platforms to a warning As discussed on D9671#146704 this lowers the error to a warning. Differential Revision: https://phab.mercurial-scm.org/D9852

purge: move extension into core mercurial The motivation is simple: it's nicer to avoid gating basic functionality. To reduce the risk of people shooting themselves in the feet, `--confirm` is now the default, unless the extensions is loaded.. For review of the body of the purge command, use this instead of what hg/phabricator will show (the block of code is modified, not just moved): Differential Revision: https://phab.mercurial-scm.org/D9820

purge: also deal with directory with --confirm Getting the exact number is simple (you have to project the result of previous deletion to detect super-directory with only about-to-be-deleted content). So we use a vaguer message. Differential Revision: https://phab.mercurial-scm.org/D9819

purge: add a --confirm option The options provide a prompt to the user before permanent deletion are made. The prompt is currently not aware of directory deletion. I'll fix this in the next changesets. Differential Revision: https://phab.mercurial-scm.org/D9818

filemerge: add a hacktastic version of internal:merge3 for merge diffs This is a version of merge3 that always reports success, so that conflict markers get preserved without us having to implement conflict storage for in-memory merge. Credit to martinvonz for the idea. The only planned consumer of this "merge tool" is my upcoming merge-diffs functionality, though I suspect it could be useful in other ways. Differential Revision: https://phab.mercurial-scm.org/D8515

rebase: add a config knob for forcing in-memory rebasing Use it in a test case where we know the rebase should proceed without incident in-memory, so we can see tracebacks rather than fallbacks. This makes it easier to try and debug when things are broken. Differential Revision: https://phab.mercurial-scm.org/D8623