Also tweak the dataChanged() api to have the client supply a package name. We
don't necessarily TRUST this, but we use it to narrow the set of packages requesting
a backup pass, no longer blithely scheduling a pass for all packages associated
with the caller's uid.
This change adds a sketched outline of the backup system architecture, with
all of the major pieces represented other than client-side helpers for
specific types of data. IBackupManager and BackupService are public so that
we can write test apps against SDK-domain symbols from the outset.
What code exists in this change hasn't been tested and may crash. It's the
beginnings of the real implementation but of course is barely begun.
