change ownership of variable & persistence

[flip111]

It would be handy if there was a convenience function that is equivalent to the following:

1. create a new() variable with owner true and/or persistence true
2. read out some value over the FFI with the same type as in step 1
3. memcpy 2 into 1
4. (optionally ??) free 1

That way things calculated by an extension can be freed immediately and the new php variable passed around as is convenient for it's lifetime