[O] least recently clocked open task in a file

[Daniel Clemente]

  I have many open tasks in a file, and I want to work a bit on each, one after 
another, without neglecting any. That would be a round-robin approach.

  But how can I find the oldest clocked-out open task in a file?
  Can I order the agenda by recentness?

  I found org-clock-history but it can't be limited by subtree/file/region, 
must be turned on work manually and would not work for tasks clocked before it 
was turned in.


Daniel