rbtree 2.1 compat

rbtree.patch

diff --git a/extconf.rb b/extconf.rb
index 9f6f0c7..674eb08 100644
--- a/extconf.rb
+++ b/extconf.rb
@@ -9,6 +9,7 @@ have_header('ruby/st.h')
 have_func('rb_exec_recursive', 'ruby.h')
 have_func('rb_exec_recursive_paired', 'ruby.h')
 have_func('rb_proc_lambda_p', 'ruby.h')
+have_func('rb_obj_hide', 'ruby.h')
 if Hash.method_defined?(:flatten)
   $defs << '-DHAVE_HASH_FLATTEN'
 end
diff --git a/rbtree.c b/rbtree.c
index 1f10fea..a7e0d5b 100644
--- a/rbtree.c
+++ b/rbtree.c
@@ -752,7 +752,11 @@ static void
 copy_dict(VALUE src, VALUE dest, dict_comp_t cmp_func, VALUE cmp_proc)
 {
     VALUE temp = rbtree_alloc(CLASS_OF(dest));
+#ifdef HAVE_RB_OBJ_HIDE
+    rb_obj_hide(temp);
+#else
     RBASIC(temp)->klass = 0;
+#endif
     DICT(temp)->dict_compare = cmp_func;
     CMP_PROC(temp) = cmp_proc;
 
@@ -1289,7 +1293,11 @@ rbtree_to_hash(VALUE self)
     
     hash = rb_hash_new();
     rbtree_for_each(self, to_hash_i, (void*)hash);
+#ifdef RHASH_SET_IFNONE
+    RHASH_SET_IFNONE(hash, IFNONE(self));
+#else
     RHASH_IFNONE(hash) = IFNONE(self);
+#endif
     if (FL_TEST(self, RBTREE_PROC_DEFAULT))
         FL_SET(hash, HASH_PROC_DEFAULT);
     OBJ_INFECT(hash, self);