[DRE-maint] Bug#561839: edit-json: prettify_json fails on input that edit_json can open

[Laurent Arnoud]

This is not an edit-json bug, this comes from libjson-ruby1.8

>> require 'json'
=> true
>> require 'open-uri'
=> true
>> JSON.parse(open('foo.json').read)
JSON::NestingError: nesting of 20 is too deep
        from /usr/lib/ruby/1.8/json/common.rb:122:in `parse'
        from /usr/lib/ruby/1.8/json/common.rb:122:in `parse'
        from (irb):3
        from :0
>>

It's seam upstream change download page to http://www.ping.de/~flori/, so watch
file is not valid anymore.

Laurent