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

changegroup: update comment Gratuitous fix, I stumbled upon this comment while reading code. Differential Revision: https://phab.mercurial-scm.org/D10339

re2: adjust local variable assignment scope Pytype flagged the exception handler where these are used as `[name-error]`, and PyCharm complained they may be used before assignment. Differential Revision: https://phab.mercurial-scm.org/D10376

rhg: Make `files` work on repo-relative paths when possible When the current directory is outside of the repository we need to turn everything into absolute filesystem paths in order to compute correct relative paths. This was previously done unconditionally, but is not necessary when the current directory is inside the repository. With this change `rhg files > /dev/null` at the root of a mozilla-central snapshot goes from ~150 ms to ~70 ms. My repository is located at a somewhat long path though (93 bytes). The effect may not be as pronounced at a shorter path. Differential Revision: https://phab.mercurial-scm.org/D10200

split: avoid strip if split is a no-op (identical to original) Differential Revision: https://phab.mercurial-scm.org/D10389