model: simplify guess_instance invocations The second argument to the guess_instance classmethod is in practice fixed for Gist, Permission, RepoGroup, Repository, User, UserGroup; so might as well move this logic into per-class specializations of guess_instance.

pytest ~= 3.0
pytest-runner
pytest-sugar>=0.7.0
pytest-catchlog
WebTest<2 # this is also a Pylons dependency and pinned in setup.py to avoid version conflicts for WebOb
mock
sphinx