Instead of keeping track of the old adjustment.upper keep track of the
old adjustment.value that corresponded to the bottom scroll position.
This fixes the integrated chatview not always scrolling to the bottom
by removing the assumption that page_size is constant between updates,
which is not the case as the view is presented in various different ways.
https://bugzilla.gnome.org/show_bug.cgi?id=686571
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
