#16 Add support for OR operator for 'use-validation-set'

[Dan Shellman]

Add the ability to define a logical OR operator across a set of 'use-validation-set' elements. Effectively, this would provide the ability to have only one of the contained 'use-validation-set' calls return without exception to successfully validate the object graph. If all in the set failed, but one succeeded, then the set would be successful.