Transparent Mem.alloc.

Lemma mem_free_contents:
forall m m2 lo hi b
(Hfree: Mem.free m b lo hi = Some m2),
forall b' ofs,
Maps.ZMap.get ofs (Maps.PMap.get b' (Mem.mem_contents m)) =
Maps.ZMap.get ofs (Maps.PMap.get b' (Mem.mem_contents m2)).