pyjarray memory leak fixes

I messed up the first commit but it doesn't seem possible to roll back once it's pushed into the repo.  So just by undoing the changes and putting the undo on the next commit, it appears that you won't pull in the messed up changes?

Our system is heavy on numpy usage and therefore light on the pyjarray usage, so it's possible I am misunderstanding pyjarray_release_pinned and you don't want that change.  I can't remember why I put that in.

I also don't remember how I determined pyjarrayiter_next was leaking, but a simple test of infinitely looping over the pyjarray, over and over again, will probably show the memory climbing.