Help with SET NULL/SET NOT NULL

Hi all,

I did an initial patch for ALTER TABLE / SET NULL that should just say 'not
implemented' when someone tries it, but I get this:

template1=# alter table test alter column a set null;
ERROR: parser: parse error at or near "null"
template1=# alter table test alter column a set null_p;
ERROR: parser: parse error at or near "null_p"
template1=# alter table test alter column a set not null;
ERROR: parser: parse error at or near "not"

What have I missed?

All regression tests pass...

Attached is context diff

I'm pretty sure that I haven't done preproc.y correctly either...

Chris

ps. DON'T COMMIT THIS PATCH!!!