pull: use `stepsdone` instead of `todosteps` The push process uses a `stepsdone` attribute instead of a `todosteps` one (with the logic swapped). We unify the two process by picking the `stepsdone` version. I feel like `stepsdone` better fits extensions that would want to extend the push exchange process.

pull: make discovery phase extensible We apply the same approach as for push and make the discovery extensible. There is only one user in core right now, but we already know we'll need something smarter for obsmarkers. In fact the evolve extension could use this to cleanly extend discovery. The main motivation for this change is consistency between push and pull.

sshpeer: forward stdout of remote "hg init" to appropriate output channel Otherwise, commandserver channel could be corrupted.

revlog: support importing censored file revision tombstones This change allows a revision log to not fail integrity checks when applying a changegroup delta (eg from a bundle) results in a censored file tombstone. The tombstone is inserted as-is, so future integrity verification will observe the tombstone. Deltas based on the tombstone will also remain correct. The new code path is encountered for *exactly* the cases where _addrevision is importing a tombstone from a changegroup. When committing a file containing the "magic" tombstone text, the "text" parameter will be non-empty and the checkhash call is not executed (and when committing, the node will be computed to match the "magic" tombstone text).

verify: report censored nodes if configured policy is abort

context: handle censored data in an on-disk file context based on config Two possible behaviors are defined for handling censored data: abort, and ignore. When we ignore censored data we return an empty file to callers requesting the file data.

manifest: add fastdelta method to manifestdict This is another step closer to alternate manifest implementations that can offer different hashing algorithms.

manifest: move _search to module level and rename to _msearch The rename is intended to provide a slight hint that it is manifest-specific.

manifest: move manifestdict-to-text encoding to manifest class A future patch will introduce a new format, with a new class.

localrepo: access status fields by name rather than index