GroupType.union(Type toMerge, boolean strict) does not honor strict parameter

This is the code as it currently stands in master:

```Java
@Override
protected Type union(Type toMerge, boolean strict) {
if (toMerge.isPrimitive()) {
throw new IncompatibleSchemaModificationException("can not merge primitive type " + toMerge + " into group type " + this);
}
return new GroupType(toMerge.getRepetition(), getName(), mergeFields(toMerge.asGroupType()));
}
```

Note the call to `mergeFields` omits the `strict` parameter. I believe the code should be:

```Java
@Override
protected Type union(Type toMerge, boolean strict) {
if (toMerge.isPrimitive()) {
throw new IncompatibleSchemaModificationException("can not merge primitive type " + toMerge + " into group type " + this);
}
return new GroupType(toMerge.getRepetition(), getName(), mergeFields(toMerge.asGroupType(), strict));
}
```

Note the call to `mergeFields` includes the `strict` parameter.

I would work on this myself, but I'm having considerable trouble working with the codebase (see e.g. http://stackoverflow.com/questions/31229445/build-failure-apache-parquet-mr-source-mvn-install-failure). Given the (assumed) simplicity of the fix, can a seasoned Parquet contributor take this up? Cheers.

**Reporter**: [Michael MacFadden](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=michael) / @mallman

_{**Note**: *This issue was originally created as [PARQUET-390](https://issues.apache.org/jira/browse/PARQUET-390). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}

Recherchez dans la base de code Parquet Java GroupType.union(Type toMerge, boolean strict), puis examinez comment mergeFields est appelé depuis cette méthode. Confirmez que la valeur de strict est propagée comme décrit et exécutez les tests pertinents du projet afin de vérifier le comportement de la fusion de schémas en mode strict et non strict.

Rédigé par le modèle d'indexation à partir du texte de l'issue.