Differenciate between failure in script from critical and non-critical packages
When some script (postinst, prerm,..) fails then we should (and I hope that we do) print error to user. But it's more or less warning in this sense. If some tiny package fails it's postinst then it should be warning. But that is not same if kernel fails its postinst. So all packages requested as critical should result to error to be reported to user but anything else should be warning.