Update SA1302 (InterfaceNamesMustBeginWithI) to handle conflicting names

The following code results in an SA1302 warning. If the code fix is applied, it introduces a new compiler error.

``` csharp
public interface Foo { }
public interface IFoo { }
public class Bar : Foo { }
```

We first need to decide how we want to handle this case (and similar), followed by implementation and tests.
