contrib: simplify the genosxversion.py command to find the hg libraries I forget what problem I ran into while trying to teach the makefile to use a non-system python. (It might have ben missing hg-evolve and/or keyring, but `check_output()` was raising an error.) This still isn't great because it will return non zero for something like the username not being set, even though we aren't asking for it. But I suppose it's still useful to simplify. Differential Revision: https://phab.mercurial-scm.org/D6753

interfaceutil: move to interfaces/ Now that we have a dedicated folder for interfaces, let's move interfaceutil there. Differential Revision: https://phab.mercurial-scm.org/D6742

interfaces: create a new folder for interfaces and move repository.py in it I was trying to understand current interfaces and write new ones and I realized we need to improve how current interfaces are organised. This creates a dedicated folder for defining interfaces and move `repository.py` which defines all the current interfaces inside it. Differential Revision: https://phab.mercurial-scm.org/D6741