Attached is a patch containing the addition of a Mojo for printing out what properties are being used by mvn. I am not completely sure I have covered all properties, but I think it hits the majority of properties I am interested in (System, POM, filters). I welcome other suggestions.
I have added in the plugin testing harness (which was non-existent for the Help plugin) but was not able to get the basic test to pass. So, I would appreciate some help in setting this up so that the help plugin can properly test itself. I followed the directions on http://maven.apache.org/developers/committer-testing-plugins.html but I must be missing something, since it can't find the necessary plugin components.
This is my first mvn patch, so please let me know any and all changes that need to be fixed in order to get it committed.