bundle2: update part creators to ``addparam`` when relevant In some cases, the use of ``addparam`` makes code much clearer.

bundle2: introduce a ``addparam`` method on part We make it easier to add new parameters after the part creation. As for the ``data`` attribute we make sure the part generation has not begun yet.

bundle2: the ability to set ``data`` attribute of the part is now official We make it safe to set the data attribute after part creation. It is an allowed operation as long as the part has not started to be generated.

bundle2: introduce a ReadOnlyPartError exception As we will introduce functions to alter already created parts, we need a proper exception to raise when code tries to alter a part that cannot be altered anymore.

bundle2: warn about error during initialization in ``newpart`` docstring As we are moving toward being able to alter a part after its creation, we need to make the implication of the part being already part of the bundle2 clear.

bundle2: track life cycle of parts We introduce a ``_generated`` attribute on parts. Coming changesets will make it easier to update a part's contents after its creation. We need a way to track if the part is still open to modification or if it is currently being generated and should not be touched anymore. As a bonus, we can now detect and crash if someone manages to write bogus code to get a part generated twice.

bundle2: update all ``addpart`` callers to ``newpart`` The new method is what we want in all current cases.

bundle2: have ``newpart`` automatically add the part to the bundle The created part is automatically added to the bundle as this is most certainly the intent of the user code.

bundle2: add a ``newpart`` method to ``bundle20`` Creating new parts is the most common operation people do when exposed to a bundler. We create a dedicated method on the bundler object for it. This will simplify the code and also avoid having to import the ``mercurial.bundle2`` module in multiple places. One part creators have been updated for testing purpose.

bundle2: small doc update on the bundler The `bundle20` class contains methods to help define the content and methods to generate the actual stream. We add small doc headers to help distinguish between the two.

localrepo: replace status method with a shim The path of the righteous man is beset on all sides by the inequities of the selfish and the tyranny of evil men. Blessed is he, who in the name of charity and good will, shepherds the weak through the valley of darkness, for he is truly Mercurial's keeper and the finder of robust methods. And I will strike down upon thee with great vengeance and furious anger those who would attempt to poison and destroy Mercurial's codebase. And you will know my name is the Lord when I lay my vengeance upon thee.

workingctx: have status method call super instead of customized code. The old code is unneeded now that basectx has the ability to calculate the status between two context objects. Now, we use the objected oriented pattern called 'super'.

basectx: copy localrepo.status method Now that all the pieces are in place, we copy the status method from localrepo. In the next few patches, we will remove the old implementation.

committablectx: cache _status in _poststatus A future patch will remove the old workingctx.status which caches the status of the working directory, therefore we now cache this status in the poststatus hook of committablectx.

committablectx: simplify caching the status Previously, workingctx had custom variables for the unknown, ignored, and clean list of files of status. These then got moved to committablectx and, after the refactoring of localrepo.status, are no longer needed. We, therefore, simplify the whole mess. As a bonus, we are able to remove the need for having 'assert'.

localrepo: remove cache code now handled by _prestatus This patch removes the last of the 'working' variable that was sprinkled throughout localrepo.status which paves the way for future patches to use the object oriented design of contexts to handle calculating the status.

workingctx: add note about super._prestatus calling manifest

basectx: preserve loading the cached manifest in _prestatus This is just a copy from localrepo.status and is a small step to removing that method entirely. The prestatus hook is only called for changectx's, thereby ensuring that the same behavior is guaranteed.

localrepo: use new subrev method of context.py With the machinery in place, we use context.subrev instead of testing for a workingctx directly. This allows more flexibility for later patches that will add memctx to the mix.

committablectx: add subrev method to return None This allows a future patch to use object oriented style to remove an if statement in the status method.

basectx: add subrev method to return the rev of a subrepo given a subpath This will be used in an upcoming patch to simplify the status method by eliminating an if block.

merge with stable

bundle2: fix bundle2 pulling all revs on empty pulls When bundle2 was enabled, if hg pull had no commits to pull, it would print 'no changes found' and then download the entire repository from the server. This was caused by heads and common being set to None, which gets treated as heads=cl.heads() and common=[nullid], which means download the entire repo. Pulling bundles without a changegroup is a valid use case (like if we're just updating bookmarks), so this modifes the bundle code to allow not adding changegroups. This is backport of ab5040cd5749.

exchange: fix bad indentation Those two lines where double indented for no good reasons. This is backport of 71931b789424.