rhg: add a limited `rhg files` subcommand Differential Revision: https://phab.mercurial-scm.org/D8869

rhg: add a `Files` `Command` to prepare the `rhg files` subcommand Differential Revision: https://phab.mercurial-scm.org/D8868

rhg: simplify `FindRootError` handling Differential Revision: https://phab.mercurial-scm.org/D8867

rhg: add buffered stdout writing possibility Improve batch stdout writing performance. At some point line buffered output should be introduced. Differential Revision: https://phab.mercurial-scm.org/D8866

rhg: ask the error message from `CommandError` Avoid repeating the display of the same error messages in different commands. Differential Revision: https://phab.mercurial-scm.org/D8865

rhg: Do not return error when when we really mean ok in commands Before when a command was successfull `Err(CommandErrorKind::Ok.into())` was returned which is an oxymoron. Using `Ok(())` when everything is ok seems more appropriate. Differential Revision: https://phab.mercurial-scm.org/D8864

hg-core: define a `ListTrackedFiles` `Operation` List files under Mercurial control in the working directory. Differential Revision: https://phab.mercurial-scm.org/D8863

hg-core: remove the `Operation` trait There is no way to currently define a trait which can both return references to `self` and to passed data, which is what we would need. Generic Associated Types may fix this and allow us to have a unified interface. See: rust #44265 Differential Revision: https://phab.mercurial-scm.org/D8862

hg-core: make parse_dirstate return references rather than update hashmaps Returing a vec is faster than updating a hashmap when the hashmap is not needed like in `hg files` which just list tracked files. Returning references avoid copying data when not needed improving performence for large repositories. Differential Revision: https://phab.mercurial-scm.org/D8861

repository: introduce constant for internal phase repo requirement and use it In future we will like to much cleaner logic around which requirement is for working copy and which can go in store. To start with that, we first need to de-clutter the requirement values spread around and replace them with constants. Differential Revision: https://phab.mercurial-scm.org/D8912

repository: introduce constant for sparse repo requirement and use it In future we will like to much cleaner logic around which requirement is for working copy and which can go in store. To start with that, we first need to de-clutter the requirement values spread around and replace them with constants. Differential Revision: https://phab.mercurial-scm.org/D8911

localrepo: refactor `.hg/requires` reading logic in separate function In an upcoming patch, we will be reusing this to read `.hg/store/requires`, so let's separate it in a different function before. Differential Revision: https://phab.mercurial-scm.org/D8910

localrepo: refactor logic to calculate sharedvfs in separate fn We will be reusing this in an upcoming patch, so better to refactor it into a separate function. Also the underlying handling deserves a function of it's own. Differential Revision: https://phab.mercurial-scm.org/D8909

store: refactor space delimited list to proper data structure There is no good reason why are having a space delimited list and then using `.split()` to get the actual list. Let's convert this into a proper collection. Differential Revision: https://phab.mercurial-scm.org/D8908

makefile: stop setting unused HGEXTDIR variable during osx build The variable was added in a38ed42cd23c (osx: include chg by default, 2017-03-20), but I can't find any others references to the variable in that commit or in any other commits. Differential Revision: https://phab.mercurial-scm.org/D8915

merge: drop commitinfo argument to applyupdates (API) We now pass the mergeresult object and hence there is no need to have a separate commitinfo argument as the required info is present in mergeresult object. Differential Revision: https://phab.mercurial-scm.org/D8904