dispatch: ignore failure to flush ui When the pager dies, we get a `SIGPIPE`. That causes `error.SignalInterrupt` to be raised ` (from `ui._catchterm()`). Any further writes or flushes will cause further `SIGPIPE`s and furhter `error.SignalInterrupt`. If we write or flush outside of the try/except that handle `KeyboardInterrupt` (which `error.SignalInterrupt` is a subclass of), then control will escape from the `dispatch` module. Let's fix that by ignoring errors from flushing the ui. I would have rather fixed this by restoring the stdout and stderr streams when the pager dies, but it gets complicated because of multiple ui instances (ui/lui) and different pager setups between regular hg and chg. This changes a test in `test-pager.t`, but I don't understand why. I would have thought that all the output from the command should have gone to the broken pager. Differential Revision: https://phab.mercurial-scm.org/D11627

dispatch: don't change error status if flushing stdio fails If we already have a non-zero exit code, I don't think we should change it to 255 because we fail to flush stdio. This may not matter yet, but it will matter when I make a killed pager result in exit code 250 (it's currently 255). Differential Revision: https://phab.mercurial-scm.org/D11626

dirstate-v2: Use "byte sequence" in docs The patch originally sent as https://phab.mercurial-scm.org/D11546 used "byte string" but that was changed during review to avoid suggesting Unicode or character encodings. However "byte range" sounds to be like a range of *indices* within a byte string/sequence elsewhere. This changes to "byte sequence". Python docs use "sequence" a lot when discussing the `bytes` type: https://docs.python.org/3/library/stdtypes.html Differential Revision: https://phab.mercurial-scm.org/D11623

rust: Make the hg-cpython crate default to Python 3 This default is used when running `cargo` manually such as for `cargo test`. `setup.py` and `Makefile` both configure the Python major version explicitly. Differential Revision: https://phab.mercurial-scm.org/D11618