Previously, all packages on the image, both activated and unactivated,
were in $systemPackages, so if a package actually in /system/packages
had a dependency in the Installer optional package area, the dependency
checking would see no problem but the generated image would be broken.
Now, packages going into /system/packages are treated separately
from those going elsewhere, and error checks added so the above
condition will not occur.
(I ran into this while working on the build-package upgrade
in the following commits.)
dd419e59dc