Issue: redefinitions and order-significance

With one exception, the order of definitions in a <grammar> element is
not significant.  The exception is that the ability to redefine with the
combine attribute on <define> makes the order of <include> elements
significant.

One possibility would be require that <define> elements that redefine or
combine with other definitions should go inside the <include> elements
that includes the pattern that contains the original definition. 
Instead of

<grammar>

  <include href="addressBook.trex"/>

  <define name="card.local" combine="replace">
    <optional>
      <element name="note">
        <anyString/>
      </element>
    </optional>
  </define>

</grammar>

you would do:

<grammar>

  <include href="addressBook.trex">

    <define name="card.local" combine="replace">
      <optional>
        <element name="note">
          <anyString/>
        </element>
       </optional>
     </define>

  </include>

</grammar>

There's more to say here, but for now I just want to get this in the
issues list.

James