dependency-ordered incremental execution of scripts

[trusktr]

It'd be nice to have depnedency-ordered incremental runs. F.e. having multiple packages where a command needs to be ran in certain packages first in order for subsequent run in dependent packages to succeed. And on second run of mono-run of a specific script, it'd be nice for it not to run the script for packages that haven't changed (perhaps by supplying mono-run an option like --incremental).