Fix to special case Dispose method to be treated as non-action

#1294
@rynowak @yishaigalatzer 
I don't think that the string-based checks are really going to bite you, but it's more precise to do something like this.

```
var typeInfo = methodInfo.DeclaringType.GetTypeInfo();
return 
    typeof(IDisposable).GetTypeInfo().IsAssignableFrom(typeInfo) &&
    typeInfo.GetInterfaceMap(typeof(IDisposable)).TargetMethods[0] == methodInfo;
```
This effectively says "is the current method that implementation of IDisposable.Dispose"

Using the string has the effect of blocking *All* methods called Dispose on the class. I'm not sure yet if I think that's better or worse.