pip install script warnings should ignore dirname(sys.executable)

[pradyunsg]

From #4553 (comment)

this is a common use case this PR did not cover.

if the executable is installed in dirname(sys.executable), we can skip the warning. Basically, treat dirname(sys.executable) as being a directory on PATH.

The "use case" above, is of installation using venv/bin/pip when invoking without activating a virtualenv.

@pfmoore doesn't feel strongly either way. @ncoghlan is in favour.

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.