Add NameError#name. Fix NameError.new and NameError.initialize. Enable 2nd argument for NameError.new in C API.

mrblib/error.rb

@@ -38,6 +38,16 @@ end
 
 # ISO 15.2.31
 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)
+  end
 end
 
 # ISO 15.2.32

src/error.c

@@ -306,8 +306,8 @@ mrb_name_error(mrb_state *mrb, mrb_sym id, const char *fmt, ...)
   argv[0] = mrb_vformat(mrb, fmt, args);
   va_end(args);
 
-  argv[1] = mrb_symbol_value(id); /* ignore now */
-  exc = mrb_class_new_instance(mrb, 1, argv, E_NAME_ERROR);
+  argv[1] = mrb_symbol_value(id);
+  exc = mrb_class_new_instance(mrb, 2, argv, E_NAME_ERROR);
   mrb_exc_raise(mrb, exc);
 }