cubicweb-vcsfile #2818315 hg changesets can be pulled without corresponding obsolete markers [validation pending]

hg pushes changesets and markers in separate transactions, so it's possible a pull would get the changesets without the markers. We should try and work around this race condition.

prioritynormal
typebug
done in1.12.3
load left0.000
closed by#30c4d7f961d3 [hg] hack around race condition between pulling changesets and obsolete markers
patch[hg] hack around race condition between pulling changesets and obsolete markers [applied]