Merge branch 'release/0.83.8' into develop
update slow queries doc & manual indexes.
avoid workers to communicate. it just fails, with too many heartbeats missed.
Add the core social_pipeline.
Update stats on article delete.
Feeds get a new stat: the open feed number.
Use the QS method, Luke!
more usefull manual (partial) indexes on big tables.
We're benchmarking mongodb stats, not reldb.
obsolete comments removal.
Social auth debug (with no luck).
Take None in account for bookmarks.
Import sparks mixins from the mixins sub-module (needs sparks develop / 4.12).
fix the social pipeline debug().
Enhanced admin for articles (faster). Still, duplicate filter doesn't worK.
Reorganize social-auth configuration. Still, no luck with login (but association is OK).
css for twitter feeds.
Comments & docstrings in check functions. I need to display them from shells.
avoid a warning.
Fix 2 import misses. These views are probably still not rel-db complete, but that's a catch.