StorageRef inside Pointer is almost useless.

[vitvakatu]

I suggest to replace it with some uid

[kvark]

Upon further inspection, it appears that you are right - it's not used for anything other than keeping the storage alive and verification. Since we can't do much without the storage anyway, we can replace the verification with some UID and be happy with it.

The change would have some far-fetching consequences, actually:

1. faster Pointer creation/cloning, as well as storage locking
2. no need for StorageRef with its Arc<RwLock<Storage>>> any more
3. simpler UpgradeErr

[kvark]

Also please note that this issue is in direct conflict with #7