ALTER TABLE fixes (take two)

Hi all,

Following Tom's guidance (as best I could) I have a much better
patch for fixing the ALTER TABLE woes. It properly handles renaming
tables and columns under every circumstance I've tested -- including
self-referential FK/PK.

First patch is to move defines around so I can get to them from the
rename.c file.

Second patch adds the update_ri_trigger_args() function which is called
from renameatt() and renamerel() to keep the pg_trigger.tgargs in sync
with the renamed att/rel.

cheers.
brent

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