Systemd-for-the-user-session would also do this, but that's a deeply
invasive change that I may not actually get to this cycle.  This
change is tiny and non-invasive, but provides an important benefit:
You can actually reliably tell *which* applications are logging which
messages (assuming they're launched by the shell).

This actually complements a recent change in DBus: See
https://bugs.freedesktop.org/show_bug.cgi?id=54445 which does a
similar thing for bus activated apps.