So we have several nasty issues when using ignore-spm-downgrades here.
First of all, calculate_world_updates should get the setting directly from
SystemSettings instead of bugging developer asking for it.
Secondly, calculate_world_updates should return a 4D tuple, also containing
the matches ignored when ignore-spm-downgrades is enabled.
Moreover, Spritz packages.py getPackageItem featured an unused argument,
which has been dropped.
I know this commit is a bitch because we are talking about changing API
and affecting several files at once.
5ec9677460