* class.c (rb_singleton_class_clone): Qnil must be used for a null
	  class reference when we use NIL_P() to check class reference
	  validity.  The bug was exposed by the spec test of Sequel.
	* eval.c (ruby_init): Use NEW_CREF().


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_8_7@24843 b2dd03c8-39d4-4d8f-98ff-823fe69b080e