Add generate_deltas storage parameter for tables and matviews.
Call AfterTriggerSaveEvent when generate_deltas is set.
Avoid unnecessary work for generating deltas case.
Add comment about timing of delta tuplestore creation.
Fix comment.
Further improve comment.
Create, drop, and load delta tuplestores.
Pass the delta tuplestores through the TriggerData structure.
Merge branch 'master' into afterstmt
Fix a code comment.
Merge branch 'master' of /home/kgrittn/pg/postgresql into afterstmt
Merge branch 'master' into afterstmt
Merge branch 'master' of /home/kgrittn/pg/postgresql into afterstmt
Merge branch 'afterstmt' into transition
Revert the creation of a generate_deltas reloption.

This isn't needed if we use standard SQL syntax for CREATE TRIGGER
because we will know the specific triggers which require a delta.