Closes #551: Oracle Constraints

	* AlterDefaultConstraint implemented
	* DeleteDefaultConstraint implemented
	* Added support for SystemMethod.CurrentUser
Revert changes to IntegrationTestOptions
Merge pull request #562 of tommarien/oracleAlterDefault

* https://github.com/schambers/fluentmigrator:
  Revert changes to IntegrationTestOptions
  Closes #551: Oracle Constraints