- fix #23: connect callback on error

- allow `Batch.add()` to be called with `null` (`undefined` or non `Batch` or `Query` objects will still yield error)
- empty `Batch` objects will not attempt to execute, and will yield and empty array
- quote formatting
empty `Batch` objects will not attempt to execute, and will yield and empty array
Merge branch 'master' of https://github.com/godaddy/node-priam

Conflicts:
	test/unit/drivers/helenus.tests.js
	test/unit/drivers/node-cassandra-cql.tests.js