I like these patches; the first two are nice cleanup. My only gripe is that pgstat_get_backend_desc() is not really a pgstat function; I think it should have a different name with a prototype in miscadmin.h (next to the enum's new location, which I would put someplace near the "pmod.h" comment rather than where you put it; perhaps just above the AuxProcType definition), and implementation probably in miscinit.c.
-- Álvaro Herrera https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services