Fixes parsing writing and pass-through of integers with
higher precision than double can handle.
Note this adds extra precision compared to JavaScript, but the
JSON files read and written this way are still valid, and the extra
precision in reading and writing this way is used by many JSON
libraries.
Fixes: QTBUG-28560
Change-Id: I30b2415c928d1c34c8cb4e4c6218602095e7e8aa
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
edec095cf8