MABC should configure its clustering funcs in configure() not operator().

[brettviren]

This perhaps more about a general cleanup / refactoring of MABC.

But, specifically, the clustering "functions" (actually classes that usually but not always call functions) have no chance to validate their configuration until executed. Config should be done during the configuration phase. Doing it during execution means config errors do not show up until some possibly lengthy period of processing is done. Also, the configuration phase is meant to assure single-threaded context which this execution-time config violates.

There are various other "wrinkles" in MABC of this type that perhaps can best be smoothed out by lifting the clustering "functions" into actual DFP nodes.

Related #377