Revisions to DDL docs
Add release note on #304
Merge branch 'bug304' of github.com:ssinger/slony1-engine into bug304
Fix typo in sample data
create string_agg in slony1_base.sql not slony1_funcs.sql

If the CREATE AGGREGATE is in slony1_funcs.sql it will fail on an update functions
since the aggregate already exists.  As part of the upgrade we will check
to see if we need to create the aggregate.