su.c: run pam_getenvlist() after setup_env

su.c: run pam_getenvlist() after setup_env

When "su -l" is used the behaviour is described as similar to
a direct login. However login.c is doing a setup_env(pw) and then a
pam_getenvlist() in this scenario. But su.c is doing it the other
way around. Which means that the value of PATH from /etc/environment
is overriden. I think this is a bug because:

The man-page claims that "-l": "provides an environment similar
to what the user would expect had the user logged in directly."

And login.c is using the PATH from /etc/environment.

This will fix:
https://bugs.launchpad.net/ubuntu/+source/shadow/+bug/984390