Build process should check numpy and scipy meet minimum version requirements

[jnothman]

While we don't allow setuptools to automatically install numpy and scipy, and we recently (f41f2e4) inserted custom error checking for the case that they are not installed, we should also error out of the setup process if the minimum version requirements are not met.

[ghost]

@jnothman Looks like this issue's been fixed. I was wondering if this issue could be closed so that it doesn't show up when filtering for the need contributor label? Thanks!