compat: adjust `wrapadd` for upstream Mercurial core updated the API in f385ba70e4af.

debian: override default value for SPHINXBUILD in docs/makefile This is the recommended Debian approach. As suggested by Debian Developer Stephen Kitt, use the approach recommended by Debian for building Sphinx documentation. See https://wiki.debian.org/Python/LibraryStyleGuide#Sphinx_documentation Also belated credit to Zash on the #mercurial channel on the Freenode IRC network, who suggested the Make variable approach in the first place.

obshashtree: move obshashtree in its own module The code no longer serve a core purpose. We just keep it because the command might be useful. We move it in a dedicated module so that it does not get in the way of other work.