Diagnose test failure on sync-images branch

[rouson]

As of commit 30c8096, running fpm test on the sync-images branch yields one test failure:

 A subdomain_t
    passes on computing a correctly shaped Laplacian for a 2D flat-topped, step-like plateau.
    passes on reaching the correct steady state solution.
    FAILS on functional pattern results matching procedural results.
 2 of 3 tests pass.