Set isInTransaction to false even if close throws

If a transaction wrapper's closer throws (such as flushBatchedUpdates in ReactDefaultBatchingStrategy) then we still want to properly deinitialize the transaction by setting isInTransaction to false. Without this, we can't reuse the transaction object (in this case, all future batched updates would fail because nested transactions aren't allowed).
Merge pull request #1021 from spicyj/close-finally

Set isInTransaction to false even if close throws