merge revision(s) r46342: [Backport #9954]

	* vm.c (core_hash_merge_kwd): should return the result hash, which
	  may be converted from and differ from the given argument.
	  [ruby-core:62921] [Bug #9898]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@46619 b2dd03c8-39d4-4d8f-98ff-823fe69b080e