[build] Show an informative message when trying to run test from toplevel when disabled
[Protocol] Fix GCHandle usage for struct and disable fast path.

Mono compiler seem to have regressed(?) when it comes to taking the address of a generic struct type. This means we need to use boxed struct object to achieve the same thing with GCHandle.
[tests] Bump version number in introspection tests
[build] Bump to 0.8.1