ENH: change refCount (internal) from count() to use_count()

- allows unambiguous of count() for other classes.
  Naming as per std::shared_ptr.

STYLE: qualify use_count() and unique() methods with the refCount base

- clearer/consistent meaning

applications/test/tmp/Test-tmp.C

@@ -41,7 +41,7 @@ void printInfo(const tmp<T>& item, const bool verbose = false)
         << " movable:" << Switch(item.movable());
     if (item)
     {
-        Info<< " refCount:" << item->count();
+        Info<< " refCount:" << item->use_count();
     }
 
     Info<< " move-constructible:"