merge revision(s) r40101:

	* struct.c (make_struct): avoid inadvertent symbol creation.
	  (rb_struct_aref): ditto.
	  (rb_struct_aset): ditto.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_0_0@44968 b2dd03c8-39d4-4d8f-98ff-823fe69b080e