No longer use rel_info($rel)->{class} in the cond resolver

It turns out there are a lot of codebases there containing garbage in the
rel definition. Punt for after 0.082800 to lean up that mess.

Also be less strict on checking the foreign_values contents - downgrade
mismatches to a warning (but still hard-require ::Row ancestry)
Fix for gut-reaching travesty as reported by gbjk
Stop using Sys::SigAction in pg tests