[PATCH 00 of 16] Branchcache collaboration

[Pierre-Yves David]

This series implements the branchcache collaboration method describe in on of my
previous email.

I'm using it for a week without neither troubles not visible performance
regression on the Mercurial repo (20K changesets here)

This is the final Nails to branchmap before we can use filtering on large scale
without too much impacts.

This series includes 2 patches from Idan Kamara fixing cache issue that impacted
the collaboration.

-- 
Pierre-Yves