ndi.dataset.database_openbinarydoc only operates on files that are within the dataset's own internal session, not any of its sessions

[stevevanhooser]

ndi.dataset.database_openbinarydoc will not find documents in its sessions

The fix will have to deal with the fact that in order to close database_closebinarydoc, the session will be needed.

Perhaps make an object cleanup function so that one no longer needs to call closebinarydoc at all.