mq: when setting message in plain mode, separate it from header (issue4453) Fix inconsistent handling of plain header separation in mq patcheader - and contrary to c87f2a5a6e49, do it in the direction of having an empty line between header and description. Plain patches are like mails and should thus have an empty line between headers and body in compliance with RFC 822 3.1.

setdiscovery: avoid a full changelog graph traversal We were definitely being suboptimal here: we were constructing two full sets, one with the full set of common nodes (i.e. a graph traversal) and one with all nodes. Then we subtract one set from the other. This whole process is O(commits) and causes discovery to be significantly slower than it should be. Instead, keep track of common incrementally and keep undecided as small as possible. This makes discovery massively faster on large repos: on one such repo, 'hg debugdiscovery' over SSH with one commit missing on the client and five on the server went from 4.5 seconds to 1.5. (An 'hg debugdiscovery' with no commits missing on the client, i.e. connection startup time, was 1.2 seconds.)

ancestor: add a way to remove ancestors of bases from a given set This and missingancestors can share state, which will turn out to be perfect for set discovery.

ancestor: add a way to add to bases of a missing ancestor object This will be useful for setdiscovery, since with that we incrementally add to our knowledge of common nodes.

ancestor: add a way to test whether a missing ancestor object has bases This is pretty trivial so there's no unit test coverage for it. This will be used by setdiscovery.

ancestor: remove now-unused missingancestors function Callers should use revlog.incrementalmissingrevs instead.

revlog: switch findmissing* methods to incrementalmissingrevs This will allow us to remove ancestor.missingancestors in an upcoming patch.

revlog: add a method to get missing revs incrementally This will turn out to be useful for discovery.

test-ancestor: add support for multiple tests against one incremental object In upcoming patches we'll add more operations to the object, and this prepares for testing those operations.

test-ancestor: move naive missing ancestor algorithm into a class This mirrors the change to the real missing ancestor algorithm in a previous patch.

ancestor.missingancestors: turn into a state-keeping class This allows multiple efficient missing ancestor queries against the same set of bases. In upcoming patches we'll also define ways to grow the set of bases. The fact that the test output hasn't changed establishes this patch's correctness.

ancestor.missingancestors: calculate start point after filtering revsvisit Any revs that are filtered out are also in basesvisit, which means they wouldn't be returned in the missing list anyway. There's no need to explore such revs or their ancestors. The 'if not revsvisit' check moves down because we can't call max() on an empty set.