narrow: use `get_unique_pull_path` The narrow's `tracked` command does not support multiple destination, lets use the dedicated API then. Differential Revision: https://phab.mercurial-scm.org/D10404

urlutil: add a new `get_unique_pull_path` This function is dedicated to call that needs a single destination. Currently most caller actually need that since few actually support multiple destinations (the most importants `hg push` and `hg outgoing` do). So having a clear API point for that will be important when the time comes to have a single `[paths]` alias resolving to multiple urls. Differential Revision: https://phab.mercurial-scm.org/D10403

mq: use the new `get_clone_path` to get the remote url We stop using `ui.expandpath` to use a function with a more defined semantic. This will help us to make it an option to point [paths] entry to multiple destination. Differential Revision: https://phab.mercurial-scm.org/D10402

urlutil: add a `get_clone_path` function We add a new function with a semantic focussed on `clone` operation (so without an existing repository). I am not certain the return type is the best, but this is what we need for now. Once all caller are migrated we might start thinking about that the API should be. For now that will do. Differential Revision: https://phab.mercurial-scm.org/D10401

outgoing: use `get_push_paths` in the revset too The revsets now use the same code as everyone and is ready for entry in `[paths]` pointing to multiple entries. Differential Revision: https://phab.mercurial-scm.org/D10393

incoming: use `urlutil.get_pull_paths` Lets use the new method to increase code reuse. However I did not implement support for multiple source yet. It would be possible create multiple temporary bundle, but that is a bit too much work outside of my current route to make the detour. Differential Revision: https://phab.mercurial-scm.org/D10392

outgoing: accept multiple destinations This align the behavior of `hg outgoing` with the one of `hg incoming`. In addition this prepare the introduction of having simple `path` resolve to multiple destination in practice (eg: `default`) Differential Revision: https://phab.mercurial-scm.org/D10391

outgoing: pass subrepo path using function argument instead of abssource hack This is clearer, remove the needs for the `repo._subtoppath` hack and will make our live easier when making `outgoing` accept multiple destinations. Differential Revision: https://phab.mercurial-scm.org/D10390

subrepo: introduce a `repo_rel_or_abs_source` function The `subrepoutil` module has various function to compute the path of a sub-repository compared to the root of the top repository. However, they was no function available to compute the relative path of the repository "source". And we need this information for exchange operation (in our case, `hg outgoing`). The information is currently build using the `repo._subtoppath` hack. We reuse the same logic but in a dedicated function independent of the `repo._subtoppath` hack. Differential Revision: https://phab.mercurial-scm.org/D10434

urlutil: use bytes for Abort messages Caught by pytype. Also fix a minor grammar issue in the second message. Differential Revision: https://phab.mercurial-scm.org/D10433