tests: use forks when modifying repositories in vcs tests Otherwise other tests (primarily checking the size of the repo) would fail because they expect the repos to be unmodified.

[tox]
minversion = 1.8
envlist = py{26,27}-pytest

[testenv]
setenv =
    PYTHONHASHSEED = 0
deps =
    pytest: pytest
commands =
    pytest: py.test {posargs}