numpy: update comments
Revert "numpy: We force brewed python"

This reverts commit 18c3b556fdcad8d0b37bc091a6fc62326b12ea85.
Revert "scipy: flag to fix compilation with non-Apple gcc."

This reverts commit 93c28cd455a8eb2f63bf376a4a78edbed3e2e349.
scipy: Fix for gcc must not be added for clang

...or a lot of scipy's tests will error our (or even hang).