Final .nd2 fixes for 5.0.3

Addresses two issues:

* http://lists.openmicroscopy.org.uk/pipermail/ome-users/2014-July/004589.html, files for which are in ```nd2/karsten```; without this change both files should show 104 series, with varying numbers of timepoints.  With this change, there should be 105 series and no timepoints as shown in NIS Elements.

* Performance with large files.  I was testing with ```nd2/sara/Ex9 ALADIN WT KO KI 31_07_2013.nd2``` (the largest file we have), and setId time has now gone from ~1300s to ~500s.  See  https://trello.com/c/1ZClsqPU/42-nd2-performance.

/cc @sbesson