Adding PostgreSQL 8.3 dialect

[DavidMoore]

This would let people specify the Postgres83Dialect when configuring their ISessionFactory using FluentNHibernate.

The Postgres83Dialect in NHibernate just adds support for the PostgreSQL XML datatype:

	/// <summary>
	/// An SQL dialect for PostgreSQL 8.3 and above.
	/// </summary>
	/// <remarks>
	/// PostgreSQL 8.3 supports xml type
	/// </remarks>
	public class PostgreSQL83Dialect : PostgreSQL82Dialect
	{
		public PostgreSQL83Dialect()
		{
			//https://www.postgresql.org/docs/8.3/static/datatype-xml.html
			RegisterColumnType(DbType.Xml, "xml");
		}
	}

[DavidMoore]

@hazzik Did you want me to help look into the integration build problems?

[DavidMoore]

Cheers @hazzik! Personally there's no pressure here to get this released as yet, it's a "nice to have" feature for us. Thanks for your work.