Individual: don't always use the display_id.
Individual: don't always use the display_id.

Sometimes, a Persona's display_id will fall back to the IID, which
we really don't want to show as a display name.

Fixes bug 792567 (https://bugzilla.gnome.org/show_bug.cgi?id=792567).

pwithnall/folks,GNOME/folks,pwithnall/folks,GNOME/folks,GNOME/folks,pwithnall/folks