pypa/virtualenv — pull request #426 by alanfranz (2013-05-08 09:11:07+00:00)
Title: Prevent accidental execution instead of sourcing

A quite common error for virtualenv newcomers is to try running 'activate' instead of sourcing it; the fact it's not executable is often not enough.

This prevents the mistake without any obvious drawback to me.

The approach can be extended to other shells, but I'm quite unfamiliar with them.