PropertiesChanged signal, take 2

[David Zeuthen]

Hey Lennart,

Actually, thinking about it some more, it adds zero value having a
PropertiesChanged() signal if it is not including the value!

That is, it's not going to help any generic proxy mechanism. Either
the client-side proxy is dumb and does a Get() on every access. And we
won't need a PropertiesChanged() signal at all. And app-access (e.g.
reading the property) is blocking because we need the Get(). Otherwise
the client-side proxy is smart and does Subscribe() + GetAll() +
updates cached value on receiving signals. And the app code can do
non-blocking access. Hence, "true_no_value" actually makes no sense at
all. So I think we should just remove true_no_value from the spec!


     David