Add some improved logic to seahorse to have it gracefully fall back to insecure
memory usage for sensitive storage when gnome-keyring doesn't have the privileges
to use mlock(2)/munlock(2). This behavior is much more useful than the ungraceful
dereference of a NULL pointer (and subsequent crash of the seahorse programs) that
currently is employed.

This patch makes seahorse (and seahorse-agent, seahorse-daemon, etc.) warn the user
about having to use secure memory so that consumers such as Evolution and other
software can make use of seahorse.

A larger and more valuable project would be to provide some sort of unprivileged
user mlock(2) support in the base system. Some ideas are currently being discussed.

Reviewed by: marcus, gnome@, imp
Approved by: marcus (gnome)