Delete unused NameError#new. And add test.

mrblib/error.rb

@@ -40,10 +40,6 @@ end
 class NameError < StandardError
   attr_accessor :name
 
-  def new(message="NameError", name=nil)
-    initialize(message, name)
-  end
-
   def initialize(message=nil, name=nil)
     @name = name
     super(message)

test/t/exception.rb

@@ -42,6 +42,16 @@ assert('Exception.exception', '15.2.22.4.1') do
   assert_equal 'a', e.message
 end
 
+assert('NameError', '15.2.31') do
+  assert_raise(NameError) do
+    raise NameError.new
+  end
+
+  e = NameError.new "msg", "name"
+  assert_equal "msg", e.message
+  assert_equal "name", e.name
+end
+
 assert('ScriptError', '15.2.37') do
   assert_raise(ScriptError) do
     raise ScriptError.new