The trick is to give the virtualenv in which you build your docs access to 
the global site-packages directory -- see Advanced Settings > Use system 
packages. RTD has numpy 1.8 and scipy installed system wide.

As for testing, to ensure that you can build your docs from scratch in 
a new virtualenv (each version of the docs gets its own virtualenv), try 
deleting the build environment:
http://read-the-docs.readthedocs.org/en/latest/builds.html#deleting-a-stale-or-broken-build-environment