Re: support for CREATE MODULE

Hm. If the functional requirement is "group objects without needing
any out-in-the-filesystem infrastructure", then I could see defining
a module as being exactly like an extension except there's no such
infrastructure --- and hence no concept of versions, plus pg_dump
needs to act differently.  That's probably enough semantic difference
to justify using a separate word, even if we can share a lot of
code infrastructure.