Log Message:
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Reduce LOCK levels OF CREATE TRIGGER AND SOME ALTER TABLE, CREATE RULE actions.
Avoid hard-coding lockmode used FOR many altering DDL commands, allowing easier
future changes OF LOCK levels. Implementation OF initial analysis ON DDL
sub-commands, so that many LOCK levels are now at ShareUpdateExclusiveLock OR
ShareRowExclusiveLock, allowing certain DDL NOT TO block reads/writes.
FIRST OF NUMBER OF planned changes IN this area; additional docs required
WHEN FULL project complete.