This is heavily inspired from Eo_Id infrastructure. Main change
are that the lower bit are always guaranteed to be zero and ignored
by all function. Also it may be a little bit less efficient in some
case, but we will tune it once we have real life usage of it.
Eo won't be migrated for 1.18 to it as Eo_Id is deeply integrated
and it is quite risky to touch it so close from a freeze. This can
wait.
Bryce Harrington
Stefan Schmidt
Cedric BAIL