Several buildfarm members (crake, loach and spurfowl) are complaining
about two queries looking up at pg_class.reloptions which trigger the
validation routines for string reloptions with default values. This
commit limits the routines to be triggered only when building an index
with all custom options set in CREATE INDEX, which is sufficient for the
coverage.
Introduced by 640c198.
This includes more tests dedicated to relation options, bringing the
coverage of this code close to 100%, and the module can be used for
other purposes, like a base template for an index AM implementation.
Author: Nikolay Sharplov, Michael Paquier
Reviewed-by: Álvaro Herrera, Dent John
Discussion: https://postgr.es/m/17071942.m9zZutALE6@x200m
