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
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
Merge pull request #450 from ricardograca/master

Fix issue #447
Merge branch 'master' of git://github.com/1o1brian/sequelize into 1o1brian-master
Merge branch 'master' of git://github.com/domesticapps/sequelize into domesticapps-master
tests for enums
added failing test for values out of enum range
enum support