add explicit handling to change the typeID

the type is the only meta attribute supported by now,
thus the decision was to handle this manually, instead of
introducing a full scope for meta attributes. Unfortunately
this leads to an assymetry: while it is possible to send an
attribute named "type", which will be intercepted and used
as a new type ID, the type will not show up when iterating
or searching through attributes.

When applying a diff, the only possibility is to *insert*
a new type attribute, and we need to check and handle this
likewise manually.

src/lib/diff/gen-node.hpp

@@ -276,6 +276,12 @@ namespace diff{
           return not util::startsWith (idi.getSym(), "_CHILD_");
         }
       
+      bool
+      isTypeID()  const
+        {
+          return "type" == idi.getSym();
+        }
+      
       template<typename X>
       bool contains (X const& elm)  const;
       
@@ -624,9 +630,9 @@ namespace diff{
   
   template<>
   inline bool
-  Rec::isTypeID (GenNode const& v)
+  Rec::isTypeID (GenNode const& attrib)
   {
-    return "type" == v.idi.getSym();
+    return attrib.isTypeID();
   }
   
   template<>

src/lib/diff/tree-diff-application.hpp

@@ -168,7 +168,7 @@ namespace diff{
       void
       __expect_end_of_scope (GenNode::ID const& idi)
         {
-          if (!endOfData())
+          if (not endOfData())
             throw error::State(_Fmt("Incomplete diff: when about to leave scope %s, "
                                     "not all previously existing elements have been confirmed by the diff. "
                                     "At least one spurious element %s was left over") % idi.getSym() % *srcPos()
@@ -213,7 +213,10 @@ namespace diff{
       ins (GenNode const& n)  override
         {
           if (n.isNamed())
-            out().appendAttrib(n);
+            if (n.isTypeID())
+              out().setType (n.data.get<string>());
+            else
+              out().appendAttrib(n);
           else
             {
               out().appendChild(n);