Allow message tray sources to provide a NotificationPolicy object,
that will configure how and if the source is displayed. For notification
daemon sources, this object is hooked to GSettings.
https://bugzilla.gnome.org/show_bug.cgi?id=685926
Content-Type scanning can be super expensive. The autorun manager is meant
for local filesystems that are plugged into a USB port or similar, not
remote NFS or sshfs mounts.
https://bugzilla.gnome.org/show_bug.cgi?id=684093
Message tray sources cannot be reused after destruction, so connect
to 'destroy' signal and clear out the previous one.
Also, fix some code paths that used the autorun manager incorrectly.
https://bugzilla.gnome.org/show_bug.cgi?id=683377
Components are pieces of the shell code that can be added/removed
at runtime, like extension, but are tied more directly to a session
mode. The session polkit agent, the network agent, autorun/automount,
are all components, keyring, recorder and telepathy client are all
now copmonents.
https://bugzilla.gnome.org/show_bug.cgi?id=683156
