Another heavy refactor of the rel resolver prototype (sequel to 03f6d1f7)

Another heavy refactor of the rel resolver prototype (sequel to 03f6d1f7)

Change the return value of _resolve_relationship_condition to a 3-value
hash, with a lot of the safety logic consolidated within that method. The
best way to gauge the significance of the changes is to look at the diff
of lib/DBIx/Class/Relationship/Base.pm

Also stop returning the "noncondition-columns" in the _resolve_condition
compa-shim. The information was only used by the code removed from
::Relationship::Base, and is rather new with no evidence of use within
CPAN/DarkPAN. It can be easily added back if necessary.