Substantially condense the three-way-merge code
Substantially condense the three-way-merge code

The merge can be a generator, for brevity.  That and front-loading cleanup seriously reduces duplication!
Comments are gone; debug messages cover many.  For the rest I'm more comfortable in code now.

Also improved expression in a few places, and so on.

PeridexisErrant/python-lnp,PeridexisErrant/python-lnp