Remove diffobj as a dependency

[brodieG]

Main complication is to figure out if there is a way to automatically use diffobj if it is available without requiring at a minimum a suggests dependency. We really need to avoid this so that we can build unitizer without diffobj installed, and this should not be a big deal because the diff piece is really a separate bit.

Maybe we can have unitizer create a objects_to_diff class, and diffobj a diffPrint or diffObj method for two of those? Then diffobj enhances unitizer?

[brodieG]

Not sure this is worth it. Many of the tests have diffobj output embedded in them, so we would have to redo all of them in order to be able to truly build independent of diffobj. Something to aspire to, and something that should have been more strongly considered at the beginning.