Fix finalize of WeakRef

* gc.c (wmap_final_func): remove WeakRef object reference from the
  array.

* gc.c (wmap_finalize): remove recycled object references from weak
  map hash properly. How to get object reference from object id was
  wrong. st_delete() doesn't work properly if key and value arguments
  are same. The key of obj2wmap is referenced object and the value of
  obj2wmap is WeakRef array.

* gc.c (wmap_aset): obj2wmap should contain WeakRef array in the
  definition.

* test/test_weakref.rb
  (TestWeakRef#test_not_reference_different_object): add a test for
  above.
  [ruby-core:49044] [Bug #7304]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@37826 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/test_weakref.rb

@@ -21,4 +21,23 @@ class TestWeakRef < Test::Unit::TestCase
     ObjectSpace.garbage_collect
     assert_raise(WeakRef::RefError) {weak.to_s}
   end
+
+  def test_not_reference_different_object
+    bug7304 = '[ruby-core:49044]'
+    weakrefs = []
+    3.times do
+      obj = Object.new
+      def obj.foo; end
+      weakrefs << WeakRef.new(obj)
+      ObjectSpace.garbage_collect
+    end
+    assert_nothing_raised(NoMethodError, bug7304) {
+      weakrefs.each do |weak|
+        begin
+          weak.foo
+        rescue WeakRef::RefError
+        end
+      end
+    }
+  end
 end