[task] allow negative intervals for add_looping_task (closes #2818280)
Instead of rejecting values < 0 with a ValueError, we ignore tasks with
a negative interval. This introduce a simple way to disable task from
configuration.
Document: cubicweb-doc
Title: CubicWeb documentation
Author: Logilab
Abstract: Some base documentation for CubicWeb users and developpers
Section: Apps/Programming
Format: HTML
Index: /usr/share/doc/cubicweb-documentation/index.html
Files: /usr/share/doc/cubicweb-documentation/*.html