revset: add experimental ancestors/descendants relation subscript The relation name is 'generations' now, which may be changed in future.

revset: add experimental relation and subscript operators The proposed syntax [1] was originally 'set{n rel}', but it seemed slightly confusing if template is involved. On the other hand, we want to keep 'set[n]' for future extension. So this patch introduces 'set#rel[n]' ternary operator. I chose '#' just because it looks like applying an attribute. This also adds stubs for 'set[n]' and 'set#rel' operators since these syntax elements are fundamental for constructing 'set#rel[n]'. [1]: https://www.mercurial-scm.org/wiki/RevsetOperatorPlan#ideas_from_mpm

revset: do not compute weight for integer literal argument In x^n and x~n, n isn't a set expression. There's no need to optimize the right-hand side.

templatekw: export ui.paths as {peerpaths} It's sometimes useful to show hyperlinks in log output. "{get(peerpaths, "default")}/rev/{node}" Since each path may have sub options, "{peerpaths}" is structured as a dict of dicts, but the inner dict is rendered as if it were a string URL. The implementation is ad-hoc, so there are some weird behaviors described in the test. We might need to introduce a proper way of handling a hybrid scalar object. This patch adds _hybrid.__getitem__() so d['path']['url'] works. The keyword is named as "peerpaths" since "paths" seemed too generic in log context.

summary: fix type of empty unresolved list It was okay because tested as a boolean prior to calling len(), but looked incorrect.

vfs: rename auditvfs to proxyvfs Since we've removed mustaudit property, auditvfs has no auditing business. It's just a utility class for vfs wrappers.

streamclone: comment why path auditing is disabled in generatev1() Copied from 39c6e349dfff. I wasn't sure whether it's for optimization or suppressing unwanted error.

streamclone: close large revlog files explicitly in generatev1()

bundle2: no longer use 'retractboundary' in updatephases The new 'phase-heads' forced all added node to secret before advancing the boundary to work around the fact changesets were added as draft by default. This is no longer necessary since the changegroup part can now use the 'targetphase' parameter. Not doing this retract boundary call has a couple of advantages: * This makes implementing phases change tracking in the transaction much simpler since retract boundary can become a rare case. * Bundling secret changesets is not the norm. Exchange never does that and even for strip, the use-case is not common.Skipping the retract boundary will avoid useless work here. * Sending phase update on push can be simplified since we can rely on the behavior of 'cg.apply' for most of it. This means less phases update send for example. * We no longer needs to track and use the addednodes during unbundling. This make it possible to have multiple 'changegroup' and 'phase-heads' parts in the same bundle without them interfering with each others. The new part has not been part of any release yet so we do not offer backward compatibility yet. It is important to update this semantic before the 4.3 freeze happens.

bundle2: automatically add 'targetphase' parameter in writenewbundle If we are bundling secret changeset and the bundle will contain phase, we request the changegroup to be applied as secret. It will be useful for next patch as we are now sure that secrets changesets are applied as secret and not applied as draft then forced to secret.