Re: ltree::text not immutable?

I wrote:
> An alternative that just occurred to me is to put the no-volatile-
> I/O-functions check into CREATE TYPE, but make it just WARNING not
> ERROR. That would be nearly as good as an ERROR in terms of nudging
> people who'd accidentally omitted a volatility marking from their
> custom types. But we could leave chkpass as-is and wait to see if
> anyone complains "hey, why am I getting this warning?". If we don't
> hear anyone complaining, maybe that means we can get away with changing
> the type's behavior in 9.6 or later.

Attached is a complete patch along these lines. As I suggested earlier,
this just makes the relevant changes in ltree--1.0.sql and
pg_trgm--1.1.sql without bumping their extension version numbers,
since it doesn't seem important enough to justify a version bump.

I propose that we could back-patch the immutability-additions in ltree and
pg_trgm, since they won't hurt anything and might make life a little
easier for future adopters of those modules. The WARNING additions should
only go into HEAD though.

regards, tom lane