subrepo: introduce a `repo_rel_or_abs_source` function...
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
