******************************
*   WARNING - PLEASE TEST    *
******************************

- changed I/O so that we NEVER change vertex number ids once a mesh has
been generated (or loaded)

- removed dataIndex from MVertex: stepData in PVewDataGModel now directly
uses the vertex/element number ids. This can lead to increased memory
use in corner cases (for which PViewDataList works fine, so it's not a
big deal), but it is simpler and faster