There is a persistent shared preference which dictates whether apps
have been successfully downloaded and are ready to install. When
the `InstallManagerService` used to receive an `ACTION_INSTALL_COMPLETE`
broadcast, it would update this preference to no longer be installing.
However, this never got received in the case of F-Droid updating itself.
In that case, we need to instead wait for the system to broadcast an
`Intent.ACTION_PACKAGE_ADDED` intent. This change waits until that
point before removing the preference.
Fixes#1027.
116cb88b81