Re: allow_system_table_mods stuff

Here is a new patch after the discussion.

- Rename allow_system_table_mods to allow_system_table_ddl.

(This makes room for a new allow_system_table_dml, but it's not
implemented here.)

- Make allow_system_table_ddl SUSET.

- Add regression test.

- Remove the behavior that allow_system_table_mods allowed
non-superusers to do DML on catalog tables without further access checking.

I think there was general agreement on all these points.

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
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