Archetype templates scoped model is merged with global model

[romain-grecourt]

When model is scoped under <templates> it should not be merged with the global model.

E.g.

global.xml:

<archetype-script>
  <output>
     <templates>
          <model>
              <value key="foo">foo1</value>
          </model>
      </templates>
  </output>
</archetype-script>

main.xml:

<archetype-script>
    <exec src="global.xml" />
    <output>
        <templates>
            <directory>.</directory>
            <includes>
                <include>**/*.mustache</include>
            </includes>
            <model>
                <value key="foo">foo2</value>
            </model>
        </templates>
    </output>
</archetype-script>

When resolving global model from main.xml, the value of foo should be foo1 and not foo2.