merge revision(s) r45874: [Backport #9813]

	* class.c (rb_mod_init_copy): always clear instance variable,
	  constant and method tables first, regardless the source tables.
	  [ruby-dev:48182] [Bug #9813]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@46498 b2dd03c8-39d4-4d8f-98ff-823fe69b080e