The original coding was trying to use a TypeName as a string Value,
which doesn't work; an oversight in my commit a61fd533.  Repair.

Also, make sure we cover the broken case in the relevant test script.

Backpatch to 9.5.

Discussion: https://postgr.es/m/20170315151829.bhxsvrp75xdxhm3n@alvherre.pgsql