sugar-jhbuild: add simplejson to dependencies

[sascha_silbe]

Python 2.6 contains simplejson, so it makes sense to use it (e.g. in Typing Turtle). But for Python 2.5, we need to depend on it.
The package name is python-simplejson for Debian/Ubuntu.

[wadeb]

In Python 2.6 and 3.0 simplejson is the default 'json' module.

It's also got nice features like formatting and line / column information in error reports.

Typing Turtle uses machine generaetd + hand edited .json files for lesson content so it's important to have these features.

[tomeu]

Replying to wadeb:

In Python 2.6 and 3.0 simplejson is the default 'json' module.

It's also got nice features like formatting and line / column information in error reports.

Also, I think that the version in 2.6 already has part of it written in C for speed, though I would expect it to be a bit slower than cjson, may be good enough. We should check their compared performance in the XO.