Redstone Mapper build error if other annotations are present on field

[cgarciae]

Specifically the class looked like this

class JsonAccessCredentials implements auth.AccessCredentials
{
    @Field()
    @override
    JsonAccessToken accessToken;

    @Field()
    @override
    String refreshToken;

    ...

I got mapper errors on build and had to the the usual "comment code until it compiles" strategy. The @override annotations where auto generated by quick-fix when I was implementing the `AccessCredentials``interface. I don't really need them, but it shouldn't hurt to have them.