include script for automating comparisons of release APKs

This is useful for checking whether the build is reproducible.
make /debian/shell work for normal users too
don't set the hardware clock on shutdown, Android will take care of that
properly initialize image_path when "Internal Storage" is true
attempt to auto-detect existing internal install

This code tries to find an existing internal install, then uses that as the
default value when reading the actual pref.  This is useful for when the
app has been uninstalled and reinstalled, but the internal install is still
in place.
/debian/shell needs to also force the use of busybox's `id -u`

`id -u` must return only a single number, so busybox's id is included. This
makes /debian/shell use it when launching a login shell, so /etc/profile
can work properly.
add pretty Debian-style messages to stop-debian.sh