Added support for AWS Redshift

I added support for Redshift, issue #661, and ran some basic tests. This is based on Marc-André's fork (https://github.com/mapoulin/flyway), but applied to flyway 3, with the following differences:

* RedshiftSchema.doAllTables was simplified because Redshift does not support inheritance
* The RedshiftTable.doLock was modified to avoid a deadlock
* The DbSupportFactory no longer depends on a hard-coded substring of the host name (redshift.amazonaws.com)