* ext/json: Merge json gem 1.5.4+ (2149f4185c598fb97db1).
	  [Bug #5173] [ruby-core:38866]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_3@33123 b2dd03c8-39d4-4d8f-98ff-823fe69b080e