Mercurial branches remain in source-listing and cleanup helpers after
Subversion support was retired. SCST development now uses Git.
Remove Mercurial detection and commands together with stale Subversion
wording. Preserve the existing no-VCS source-list fallback and all Git
behavior.
Propagate patch and module-list failures, normalize the script
directory, and expand the actual Mercurial subrepository name when
matching paths. Keep the existing no-optional-patches behavior
unchanged.
Gleb Chesnokov
Bart Van Assche