SI-6120 Suppress extra warnings

Sensibility checks in refchecks were shown to be redundant.

This commit includes a mild refactor to reduce tabbage, and
uses a local var to flag that a warning has already been emitted.

The flag is used at line 1020 to 1040.

It would be better to have the checks return true if warned,
to facilitate `nonSensically || unrelatedly`, etc. But that's a lot
of elses.

Review by? @retronym ?  I bet @paulp would rise from the grave for this one.