cubicweb-vcsfile #2586293 do **not** import hg repositories by ranging on revision numbers [done]

use a "hg incoming" like method instead; current implementation is notoriously broken.

priorityimportant
typebug
done in1.10.0
load0.500
load left0.000
closed by#050c40093b7a [hg] fix import_content algorithm (closes #2586293), #dd793db3fdf9 [hg] fix computation of incoming revisions when importing a mercurial repository (closes #2586293)