Dump Hash ivars before elements

When the Hash is revived, the ivars will be set before elements.  This
is for the case when the hash setter depends on ivars set on the hash.

ext/psych/lib/psych/visitors/yaml_tree.rb

@@ -428,15 +428,6 @@ module Psych
           node = @emitter.start_mapping(nil, tag, false, Psych::Nodes::Mapping::BLOCK)
           register(o, node)
 
-          # Dump the elements
-          accept 'elements'
-          @emitter.start_mapping nil, nil, true, Nodes::Mapping::BLOCK
-          o.each do |k,v|
-            accept k
-            accept v
-          end
-          @emitter.end_mapping
-
           # Dump the ivars
           accept 'ivars'
           @emitter.start_mapping nil, nil, true, Nodes::Mapping::BLOCK
@@ -446,6 +437,15 @@ module Psych
           end
           @emitter.end_mapping
 
+          # Dump the elements
+          accept 'elements'
+          @emitter.start_mapping nil, nil, true, Nodes::Mapping::BLOCK
+          o.each do |k,v|
+            accept k
+            accept v
+          end
+          @emitter.end_mapping
+
           @emitter.end_mapping
         else
           tag = "!ruby/hash:#{o.class}"