HPCC-9556 Support #ONWARNING and fix other issues

This pull request

* Fixes #ONWARNING so it works throughout the warning processing
* Allows command line options -w<nnn>=severity to map warnings to different levels
* Adds command line warning options to archives
* Cleans up the way errors and warnings are processed, so they always go through a delegated chain of IErrorReceivers.

There is a small associated change in the ln repository