I'm OK with an unqualified "pip install --upgrade pip" retaining pip's current behaviour of always writing the unqualified script versions.

However, running "pip3 install --upgrade pip" would ideally leave the "pip" and "easy_install" scripts alone.

For "make altinstall" compatibility, we definitely need a "--altinstall" flag that only installs the fully qualified versions of pip and easy_install.

Finally, there needs to be some way to explicitly request the "pip3" style behaviour when running via -m so we can use it from ensurepip.