Add a 'clean' task to C# task list

I am sometimes encountering odd bugs where my code is behaving as if other code I have written does not exist or has not been edited. When I encounter similar situations in a C++ environment, it usually means my object files have become out of sync with my source and usually running a 'make clean' will fix it. It would be very helpful to have a similar feature in the C# tasks so that you can make sure that your bugs are actually there and not the result of out of date assemblies.