Generic Record: change semantics of the "match" operation for objects

in the first version, I defined equality to just compare the IDs
But that didn't seem right, or what one would expect by the concept
of equality (this is a long standing discussion with persistent
object-relationally mapped data).

So I changed the semantics of equaility to be "deep".
As this means possiblty to visit a whole tree depth-first,
it seems reasonable to provide the shallow "identity-comparison" likewise.
And the most reaonable choice is to use the "matches(object)" API
for that, since, in case of objects, the matches was defined
as full equality, which now seems redundant.

Thus: from now on: obj.matches(otherObj)
means they share the same IDs

src/lib/diff/gen-node.hpp

@@ -286,7 +286,7 @@ namespace diff{
       bool contains (X const& elm)  const;
       
       
-      bool matches (GenNode const& o)  const { return o == *this; }
+      bool matches (GenNode const& o)  const { return this->matches(o.idi); }  ///< @note \em not comparing payload data. Use equality for that
       bool matches (ID const& id)      const { return idi == id; }
       bool matches (int     number)    const { return data.matchNum(number);}
       bool matches (int64_t number)    const { return data.matchNum(number);}

src/lib/diff/record.hpp

@@ -511,6 +511,7 @@ namespace diff{
    *          This trickery is necessary to avoid copying a large and possibly
    *          nested object tree; this happens when applying a diff, when
    *          recursively descending into nested child objects.
+   * @todo do we have a design mismatch here??      /////////////////////////////////////////TICKET #970
    * @see tree-diff-application.hpp
    */
   template<typename VAL>