Transparent Mem.alloc.

Lemma permission_at_free_list_1:
forall m m' l b ofs
(Hfree: Mem.free_list m l = Some m')
(Hnon_freeable: ~ Mem.perm m b ofs Cur Freeable),
forall k : perm_kind,
permission_at m b ofs k = permission_at m' b ofs k.