338 exception when attempting to fake an internal method

Fixes #338.
As it turns out, the `Castle.DynamicProxy.Internal.InternalsUtil.IsAccessible(method)` checks all kinds of things, such as the access level of the method and whether the declaring type's assembly has internals visible to `DynamicProxyGenAssembly2`. However, if we have a configurable method on a fake object, the declaring method's assembly is most often `DynamicProxyGenAssembly2`, which fails the test.