object.c: no TypeError at Symbol

* object.c (special_object_p): uninterned Symbol also should not
  raise a TypeError but return itself instead, as well as interned
  Symbols.  [ruby-core:79216] [Bug #13145]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57407 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

object.c

@@ -304,6 +304,7 @@ special_object_p(VALUE obj)
     switch (BUILTIN_TYPE(obj)) {
       case T_BIGNUM:
       case T_FLOAT:
+      case T_SYMBOL:
 	return TRUE;
       default:
 	return FALSE;

test/ruby/test_object.rb

@@ -23,6 +23,8 @@ class TestObject < Test::Unit::TestCase
     assert_equal true, true.dup
     assert_equal nil, nil.dup
     assert_equal false, false.dup
+    x = :x; assert_equal x, x.dup
+    x = "bug13145".intern; assert_equal x, x.dup
     x = 1 << 64; assert_equal x, x.dup
     x = 1.72723e-77; assert_equal x, x.dup
 
@@ -51,6 +53,8 @@ class TestObject < Test::Unit::TestCase
     assert_equal true, true.clone
     assert_equal nil, nil.clone
     assert_equal false, false.clone
+    x = :x; assert_equal x, x.dup
+    x = "bug13145".intern; assert_equal x, x.dup
     x = 1 << 64; assert_equal x, x.clone
     x = 1.72723e-77; assert_equal x, x.clone
     assert_raise(ArgumentError) {1.clone(freeze: false)}