Added test BaseClassWithoutParameterlessConstructor.
Covers #6913
Xml Serialization of Base class w/o a parameterless constructor.
Removed validation code that did not allowed serialization of base classes without a parameterless constructor.
Fixes #6913.
Merge pull request #1214 from esdrubal/xmlbase

Xml Serialization of Base class w/o a parameterless constructor.