ARM API Support

[Florian Weimer]

* Joe Darcy:

> There are no source compatibility issues with making a class implement
> another interface if no new methods are added.

I think this statement permits certain exceptions.

Here's code that breaks when a class implements another interface.

class ToBeChanged implements I1 /*, I2 */ {
}

interface I1 {
}

interface I2 {
}

interface Dispatch {
    void action(I1 o);
    void action(I2 o);
}

class User {
    void use(Dispatch d, ToBeChanged o) {
        d.action(o);
    }
}

This particular case cannot happen if I2 is fresh and introduced at
the time as ToBeChanged is changed because the user could not have
written the Dispatch class.