histedit: use `get_unique_push_path` Same as for `pathbomb`, this code does not support multiple destinations yet. It might in the future, probably with code put in common with patchwork, but for now lets use the dedicated API. Differential Revision: https://phab.mercurial-scm.org/D10408

urlutil: add a new `get_unique_push_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/D10407

fetch: use `get_unique_pull_path` to retrieve the path The fetch command does not support multiple destination, so we use the new dedicated API for that. Differential Revision: https://phab.mercurial-scm.org/D10406