fix forced_ownership_handoff during resize

All resize operations remain in the ring's list of pending
changes until all complete. Prior to this change transfers would
only be triggered for the first forced_ownership_handoff operations.
Subsequent operations would only be triggered by vnode *inactivity*.

This commit modifies the use of forced_ownership_handoff during resize
to ensure that only resize operations that are still pending are in
the throttled transfer list.
Merge pull request #331 from basho/jrw-resize-foh-fix

fix forced_ownership_handoff during resize