rhg: centralize PlainInfo

rhg: central treatment of PLAIN and PLAINEXCEPT

revset: handle wdir() in `sort(..., -topo)` The last apparent usage of `repo.changelog.parentrevs` in revsets is in `children()`, but since the sets being operated on never include wdir(), it's never called with `wdirrev` and the wdir() arg on the command line is effectively ignored instead of aborting there. I'm not sure how to fix that. Before (on a clone of hg): $ python3.8 hg perf::revset --config extensions.perf=contrib/perf.py 'sort(all(), -topo)' ! wall 0.123663 comb 0.130000 user 0.130000 sys 0.000000 (best of 76) After: $ python3.8 hg perf::revset --config extensions.perf=contrib/perf.py 'sort(all(), -topo)' ! wall 0.123838 comb 0.130000 user 0.130000 sys 0.000000 (best of 75)

revset: handle wdir() in `roots()` This is already handled in `heads()`, and both are needed to determine if a set is contiguous. I'm guessing the `0 <= p` check was to try to filter out the null revision, but it looks like that comes through in the corner case of a new repo with no commits. But that was already the case, as shown by the tests. Before (on a clone of hg): $ python3.8 hg perf::revset --config extensions.perf=contrib/perf.py 'roots(all())' ! wall 0.059301 comb 0.040000 user 0.040000 sys 0.000000 (best of 100) After: $ python3.8 hg perf::revset --config extensions.perf=contrib/perf.py 'roots(all())' ! wall 0.059387 comb 0.060000 user 0.060000 sys 0.000000 (best of 100)