Merge branch 'release/0.83.6' into develop
update slow queries doc.
make stats update work.
factorize a template fragment, on the road to understand why social signin doesn't work anymore.
make the author repair script a class method for easy relaunch.
Be sure we don't add u'' to {url,content}_error, it's just annoying to have to fix this.
version bump for 0.83.7.
Merge branch 'release/0.83.7'