testr ui only supports file repositories

[Jelmer Vernooij]

testrepository/commands/__init__.py currently hardcodes the use of testrepository.repository.file.RepositoryFactory, making it impossible for other repositories (such as the samba build farm repository format) to be used. It'd be great if it could try all available repository formats and see which one is able to open the specified URL.

[Robert Collins (lifeless)]

Indeed, Uhm, I wanted to avoid the register-everything thing that bzr does, if possible, so I deferred multiple-repo-type lookup.

What I'd like to see in a patch addressing this:
 - local lookups do not load non-local repository types
 - without a lazy-importer
 - remote lookups only load probes that are plausible (e.g. if a remote repo doesn't understand sftp, an sftp url should not result in that repo's probe being loaded)

Something like:
 - a multiple-dispatch factory
 - which flattens the url scheme and uses that to load repository/<scheme> as a module
 - if we have multiple repos for (say) http, then http would be a package, and there would be a defined entry point in http that takes care of probing efficiently. e.g. by trying for url matching logic first, then request based checks.