external apidocs don't appear by default

[Christophe Combelles]

When creating a buildout with zopeproject, the site.zcml puts the package
registration before the apidoc registration:

  <include package="${package}" />

  <!-- Remove this reference to disable the APIDoc tool.
       You should do this for production -->
  <include file="apidoc.zcml" />

This means that the bookchapters of some added packages (such as z3c.*) will
never show up in the apidoc, because the <meta:provides feature="apidoc" /> will
be located **after** all the zcml:condition="have apidoc"

I suggest to move the <include file="apidoc.zcml" /> on the top of the site.zcml
by default.