allow for trapping postgres connection errors

connect() returns an event emitter which can be used to handle errors
gracefully rather than throwing an error in callback which would
terminate the entire node process
fix #334 ('include' places a "null" element to the result if no data is related)
reuse existing DAO.identifiers
Added ENUM type
Fixed a typo in PG Query Generator ENUM update
Added DataTypes require to PG and SQLite Query Generator
Fixed a typo in PG Query Generator
Added a few tests, DRY'd out some PG ENUM code
Use env dialect for migrator and sequelize spec tests.
Make tests pass for postgresql by quoting table column names with uppercases.  Also skip stored procedure unless mysql.
only double quote table names for postgres
Merge pull request #432 from clkao/patch-3

get dialect from env when not specified
mark all known dialect-specific failing tests as todo with itEventually
Merge pull request #446 from clkao/todo-tests

mark all known dialect-specific failing tests as todo with itEventually
fixes #204 thanks to @bpartridge
use native array method
Fix issue #447
Enable reusing query option objects in find
Fix bad formatting of code
Merge pull request #450 from ricardograca/master

Fix issue #447