Related to #1963

Allow problematic jobs to fail instead of commenting them out

Related to comment in #2051

Use a wrapper script to bypass check-manifest if not under git

Some time ago when we first added support for testing pytest on AppVeyor,
jobs in a build would not start immediately one after the other, as if AppVeyor
would schedule jobs from other builds (projects) in its VMs. So it made sense
at the time to reduce the number of jobs.

I have noticed in other projects that this behavior has changed, and jobs
in a build now start one after the other. Having a separate list then improves
visibility when the build fails, because we can see at a glance the failing(s)
tox environment(s).

Use one job for each tox env on AppVeyor

Docs: Added pytest promotional talk in Russian