Allow image comparison outside tests module

[maxalbert]

This is a replacement for PR #5518 (which should be closed if this is accepted). For now this PR simply removes the assert statement so that the @image_comparison decorator can be used in situations where the test does not live in a parent directory called tests (this does not apply to matplotlib but will be useful for third-party users).

In the medium term it would be good to re-think and refactor the code in _image_directories because isn't very easy to read at a glance if you don't know what's going on already, and the logic seems somewhat fragile (see #3314 for example).

[maxalbert]

There is one failure in the Travis build but it seems to be the PEP8 issue that was fixed by #5844. Not sure what's making the AppVeyor builds fail to be honest.

[tacaswell]

power cycled the PR to re-kick CI against current master.

[tacaswell]

👍 from me once travis passes. This should be non-controversial and I think be backported back to v1.5.x

[WeatherGod]

appveyor failed on a couple of the job runs with a strange error. I can't restart them.

[tacaswell]

Do not worry about appveyor too, it also lies that it passes ;)

On Wed, Jan 13, 2016 at 1:24 PM Benjamin Root notifications@github.com
wrote:

appveyor failed on a couple of the job runs with a strange error. I can't
restart them.

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#5842 (comment)
.

[WeatherGod]

Ok. Merging and backporting to v1.5.x. Do I also need to manually backport it to the v2.x branch, or will that happen on its own?

[WeatherGod]

backported to v1.5.x as 5240759

[tacaswell]

every so someone does a 1.5.x -> 2.x -> master cascade