Re: WIP: Rework access method interface

... btw, what is the point of catalog/opfam_internal.h?  I see you added
it in b488c580aef4e05f, but it seems quite useless to have split it out
as a separate header, since only commands/opclasscmds.c uses it.

My attention got drawn to it because the current patch proposes to
#include it in amapi.h, which is as thorough a subversion of the concept
of "internal header" as I can readily think of.  If we're going to do
that with it we'd definitely need to rename it.  But I'm not following
why struct OpFamilyMember needs to be exposed at all.
        regards, tom lane