Fix interface bug introduced by 162a543

Commit 162a543 introduced a bug by handing over too many interfaces
to Castle's `ProxyGenerator.CreateClassProxy` method. The intention
behind that commit apparently was to enable `mock.As<TInterface>`
even after `mock.Object` has already been called.

That change unfortunately also caused mocked class' methods that im-
plement an interface method to no longer be mocked correctly.

This commit fixes this problem by ensuring that the "internally
implemented" interfaces are not explicitly passed to `.CreateClass-
Proxy` (like it used to be done previously).

Source/Mock.Generic.cs

@@ -213,7 +213,7 @@ private void InitializeInstance()
 					this.instance = (T)proxyFactory.CreateProxy(
 						typeof(T),
 						this.Interceptor,
-						this.ImplementedInterfaces.ToArray(),
+						this.ImplementedInterfaces.Skip(this.InternallyImplementedInterfaceCount - 1).ToArray(),
 						this.constructorArguments);
 				}
 			});