AWS Redshift Support

My attempt to provide support for Amazon Web Service Redshift database ( Issue #661 ).

Redshift is based on PostgreSQL v.8.0 with unsupported features. Here is the list : http://docs.aws.amazon.com/redshift/latest/dg/c_redshift-and-postgres-sql.html

For the unit tests, I copied PostgreSQL tests and removed those testing unsupported features. Everything was green, except the locking test. Redshift documentation states that less restrictive locks are implicitly acquired during the writing operation. I went on the safe side but we could potentially let Redshift handle it.

Marc-André