If a task fails with an exception, it is retried until it
succeeds. This is contrary to what is said in the documentation: under
the "Architecture" section, heading "Broker" it says that even when a
task errors, it's still considered a successful delivery. Failed tasks
never get acknowledged however, thereby being retried after the
timeout period. See also issues #238 and #194.
This patch adds an option to acknowledge failures, thereby closing
issue #238. Issue #194 would require some more work. The default of
this option is set to `False`, thereby maintaining backwards
compatibility.
Balletie