Fixing alternatives with higher priority for converters

Closes #876.

At this time this code works fine when the application wants to override a bundled converter:

```java
public MyLongConverter extends LongConverter {}
```

But this not work:

```java
public MyLongConverter implements Converter<Long> {}
```

So this code fixes this behavior, overriding the internal converter list when a new converter was found for the same type.
Nevermind... we just need to make it clear that higher values for priorities have precedence, right now the javadoc doesn't say so.