Fix IllegalProgramException when ROS.NET source is used directly as Unity scripts
Fix IllegalProgramException when ROS.NET source is used directly as Unity scripts

The exception was thrown due to an illegal IL_code, "isinst"
I hypothesized that the issue was related to the .NET3.5-like Mono version used
	by Unity having an issue with the way "is" is used in XmlRpcValue
After replacing the usages of "is" in Get<T>() and Set<T>(T t), Unity is happy!

VICTORY

beanstalk42/ROS.NET,uml-robotics/ROS.NET