1.4 introduced a warning for overriding roles/directives from an extension (#1962).

It would be great if this could be silenced. In our case the overriding is intentional (e.g this contains a few workarounds https://github.com/astropy/astropy-helpers/blob/master/astropy_helpers/sphinx/ext/autodoc_enhancements.py), thus the warning causes unnecessary troubles for the travis docs builds (that are set to fail if any warnings come from sphinx).