VM: move next_object_after() and first_object() to aging_space (no iteration possible in nursery)

vm/aging_space.hpp

@@ -14,6 +14,21 @@ struct aging_space : bump_allocator<object> {
     starts.record_object_start_offset(obj);
     return obj;
   }
+
+  cell next_object_after(cell scan) {
+    cell size = ((object*)scan)->size();
+    if (scan + size < here)
+      return scan + size;
+    else
+      return 0;
+  }
+
+  cell first_object() {
+    if (start != here)
+      return start;
+    else
+      return 0;
+  }
 };
 
 }

vm/bump_allocator.hpp

@@ -22,21 +22,6 @@ template <typename Block> struct bump_allocator {
 
   cell free_space() { return end - here; }
 
-  cell next_object_after(cell scan) {
-    cell size = ((Block*)scan)->size();
-    if (scan + size < here)
-      return scan + size;
-    else
-      return 0;
-  }
-
-  cell first_object() {
-    if (start != here)
-      return start;
-    else
-      return 0;
-  }
-
   void flush() {
     here = start;
 #ifdef FACTOR_DEBUG