Opaque Mem.store.

Lemma storev_val_obs:
forall (mc mc' mf : mem) (f:memren)
(vptr1 vptr2: val) chunk v1 v2
(Hstore: Mem.storev chunk mc vptr1 v1 = Some mc')
(Hf: val_obs f vptr1 vptr2)
(Hval_obs_eq: val_obs f v1 v2)
(Hobs_eq: mem_obs_eq f mc mf),
exists mf',
Mem.storev chunk mf vptr2 v2 = Some mf' /\
mem_obs_eq f mc' mf'.