Re: [PATCH] Add transforms feature

Here is a new patch which addresses some of the issues you found.

> - vs SQL standard
> 
After reviewing this, there is actually no conflict with the SQL
standard, because the CREATE TRANSFORM syntax in the SQL standard uses
an additional transform group clause which I don't use.  So there is no
ambiguity.  Hence, I left the syntax unchanged.

> - function types

I changed this so that CREATE TRANSFORM requires owning the from-SQL and
to-SQL functions.

> - create or replace causes inconsistency
> 
Fixed this by adding cache invalidation in PL/Python.