pending-messages-removed is emitted for sent messages too, but we don't
include those in the _pendingMessages list. Avoid useless spew in the session
logs in that case.
https://bugzilla.gnome.org/show_bug.cgi?id=683449
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
