Updated snapshot.

Source: qtbase 786a6466e88faf25c55c626a17f5296bce564daa
Merge branch 'master' into UpdateSnapshot

This updates the checkout of QtJson from QtBase to bring in
bug fixes (most notably, some missing calls to detach() have been
added). This updates the code to the version of qtbase at
786a6466e88faf25c55c626a17f5296bce564daa.

The update is very simple -- for reference:

git checkout -b UpdateTopic

(Reset to last commit with unmodified qt sources)
git reset --hard <SHA of last update in this repo>

(Copy updated qtjson source from qtbase into this repo)

(Merge in master to apply backport fixes)
git merge --no-ff master
Merge branch 'UpdateSnapshot'
Merge branch 'master' of qt5json into qt5json-update

Change-Id: I7adea3b91528ff4b1cfe379e7f316c73ab6d957e