update json


git-svn-id: http://smarty-php.googlecode.com/svn/trunk@4888 9dce5a81-9a42-0410-99e4-3799d3902e7f
Switch trunk version to 3.1.21-dev

git-svn-id: http://smarty-php.googlecode.com/svn/trunk@4889 9dce5a81-9a42-0410-99e4-3799d3902e7f