merge revision(s) 34306:

	* ext/json/parser/parser.rl (json_string_unescape): workaround fix
	  for over optimization of GCC 4.7. [ruby-core:42085] [Bug #5888]
	  http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51862


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_2@40305 b2dd03c8-39d4-4d8f-98ff-823fe69b080e