`to_json` generates malformed json on Python 2.4-2.5 if contained single qoutes

[Jun Omae]

to_json generates malformed json on Python 2.4-2.5 if the argument is contained single qoutes. to_json uses javascript_quote because Python 2.4-2.5 don't have json library.

Python 2.4.3 (#1, Jun 18 2012, 08:55:31)
[GCC 4.1.2 20080704 (Red Hat 4.1.2-52)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from trac.util.presentation import to_json
>>> print to_json({'json': "a ' single quote"})
{"json":"a \' single quote"}

However, single quote cannot be encoded to \', according to ​http://www.json.org/.

And, jQuery.parseJSON raises SyntaxError for such a json string. This brings a problem when Trac and Trac plugins response json as contents.

[12:46:48.548] jQuery.parseJSON("{\"json\": \"a \\' single quote\"}")
[12:46:48.553] SyntaxError: JSON.parse: bad escaped character
[12:46:51.864] jQuery.parseJSON("{\"json\": \"a ' single quote\"}")
[12:46:51.868] ({json:"a ' single quote"})
[12:52:32.423] jQuery.parseJSON("{\"json\": \"a \\u0027 single quote\"}")
[12:52:32.427] ({json:"a ' single quote"})

I propose that javascript_quote encodes a single quote to \u0027 (neither ' nor \') in order to avoid \' in json text.