Per discussion with Noah Misch, the previous coding, introduced by
my commit 65377e0b on 2011-02-06,
was really an abuse of RELKIND_COMPOSITE_TYPE, since the caller in
typecmds.c is actually passing the name of a domain.  So go back
having a type name argument, but make the first argument a Relation
rather than just a string so we can tell whether it's a table or
a foreign table and emit the proper error message.