Fix for DataONE timestamp bug

https://redmine.dataone.org/issues/6010
https://trello.com/c/q3lAPAqY/246-bug-dataone-listobjects-call-doesn-t-respect-timestamps

The way I've been testing it on the VM is to create a series of three or four data packages and make calls that ask for tiny incremental timeslices. It should work now (except for some reason if the to-date is less than 0.001 seconds away from the last entry's specified date, but I'm not sure there's anything I can do about that.)

For example: `http://localhost:9999/mn/v1/object/?count=200&fromDate=2014-09-12T06:14:19.554%2b0000&toDate=2014-09-12T06:16:28.000%2b0000` on my VM returns the entry with the identifier `http://dx.doi.org/10.5072/FK2.5061.dryad.k3d62?ver=2014-09-12T06:14:58.985+00:00` but not the one with the identifier `http://dx.doi.org/10.5072/FK2.5061.dryad.s1m86?ver=2014-09-12T06:16:28.617+00:00`.