dbunit Merge Request #33: Add PostgreSQL OID data type (merged)

• Removed both TODO notes after verification, and updated the OidDataType code a bit.
• Tested locally with PostgreSQL, the integeration test passed.
• Instead of adding to SQLHelperDomainPostgreSQLIT (which is for PostgresSQL domain testing), I created another IT class PostgresSQLOidIT.
• Following SQLHelperDomainPostgreSQLIT, its IT test function is named as xtestXXX() instead of the normal JUnit testXXX(). (To avoid unit test giving errors when no database configured?)