More Metadata Iterator Improvements

* Use safe_fixtable/2 for iterators that do first/next traversal of
ets tables
* Open iterators inside the calling process. this allows iterators to
take advantage of monitoring built into ets for processes using
safe_fixtable/2 and possibly select/match_object depending on
the implementation of ets. In addition, this prevents serialization through
the metadata manager.
* Closing iterators is now mandatory for all iterator types. when an iterator,
using select/match_object has been closed that has not been fully iterated,
closing the iterator will complete the iteration. This is a definisive measure
since its is unclear if this is necessary from the ets documentation.
* Processes using remote iterators are monitored. On death, their iterators are
closed.
Fix Some Metadata Exchange Bugs

* properly merge local object with remote node
* handle missing remote object on reconcile