configure: expand PID file

This prevents the literal "${prefix}" from getting written.

https://bugzilla.gnome.org/show_bug.cgi?id=725761
NEWS: update for release
configure: bump to 3.12.1
pam: drop postlogin from fedora pam config

It's just used in practice to inflict ugly "Last Login" messages
on the GDM screen

https://bugzilla.gnome.org/show_bug.cgi?id=728281
Revert "worker: get PATH from parent instead of #define"

This reverts commit e546e4dc6649a4fdf9065322420a28fa7e666782.

It's causing problems because bindir and sbindir are in the wrong
order for a user session.
configure: change default PATH to include sbin
launch-environment: explicitly kill worker on stop even if session is running

Right now, if the launch environment is stopped while it's running the
whole process group of the session is killed. The theory is that doing
this will kill both the worker and the dbus-daemon (and anything else).

The problem is, now that gdm-simple-slave is gone, the worker is not part
of the same process group as its children, so killing the process group
of the session leaves the worker alive.

This commit makes sure the worker is always explicitly killed.

https://bugzilla.gnome.org/show_bug.cgi?id=729727