filemerge: add support for partial conflict resolution by external tool A common class of merge conflicts is in imports/#includes/etc. It's relatively easy to write a tool that can resolve these conflicts, perhaps by naively just unioning the statements and leaving any cleanup to other tools to do later [1]. Such specialized tools cannot generally resolve all conflicts in a file, of course. Let's therefore call them "partial merge tools". Note that the internal simplemerge algorithm is such a partial merge tool - one that only resolves trivial "conflicts" where one side is unchanged or both sides change in the same way. One can also imagine having smarter language-aware partial tools that merge the AST. It may be useful for such tools to interactively let the user resolve any conflicts it can't resolve itself. However, having the option of implementing it as a partial merge tool means that the developer doesn't *need* to create a UI for it. Instead, the user can resolve any remaining conflicts with their regular merge tool (e.g. `:merge3` or `meld). We don't currently have a way to let the user define such partial merge tools. That's what this patch addresses. It lets the user configure partial merge tools to run. Each tool can be configured to run only on files matching certain patterns (e.g. "*.py"). The tool takes three inputs (local, base, other) and resolves conflicts by updating these in place. For example, let's say the inputs are these: base: ``` import sys def main(): print('Hello') ``` local: ``` import os import sys def main(): print('Hi') ``` other: ``` import re import sys def main(): print('Howdy') ``` A partial merge tool could now resolve the conflicting imports by replacing the import statements in *all* files by the following snippet, while leaving the remainder of the files unchanged. ``` import os import re import sys ``` As a result, simplemerge and any regular merge tool that runs after the partial merge tool(s) will consider the imports to be non-conflicting and will only present the conflict in `main()` to the user. Differential Revision: https://phab.mercurial-scm.org/D12356

pullbundle: fix file name in the help text It is pullbundles.manifest and not pullbundle.manifest. Differential Revision: https://phab.mercurial-scm.org/D12391

unamend: abort if commit was not created by `hg [un]amend` `hg unamend` can currently undo any kind of rewrite, as long as it has an obsmarker. However, that has quite unexpected results if you run it after e.g. `hg rebase` (expecting it to behave like a generic `hg undo` command), because it updates to the predecessor and leaves the old changes in the working copy. I think it's better to allow `hg unamend` only after `hg amend` (and after `hg unamend` because that's documented as being supported). Differential Revision: https://phab.mercurial-scm.org/D12390

branching: merge stable into default

test: use `wait-on-file` in `test-racy-mutations.t` The official utility scale its timeout with the run-tests.py one. So lets use it. Differential Revision: https://phab.mercurial-scm.org/D12382

amend: fix amend with copies in extras If copy information is stored only in the commit extras and not in filelogs, then they get lost on amend if the file wasn't also modified in the working copy. That's because we create `filectx` object from the old commit in those cases, and the `.copysource()` of such objects read only from the filelog. This patch fixes it by always creating a new `memfilectx` in these cases, passing the calculated copy information to it. Differential Revision: https://phab.mercurial-scm.org/D12387