Model Report load warning message improvement (unknown model report item type)
Bug Number: n/a
Release notes (y/n): no
For Release Nums: 7.1

In preparation for merging some new model report development work, I'm 
checking in an improved warning message for an unrecognized model report 
item type:

OLD MESSAGE:
  The Model Report configuration contains an item without a specified type.

NEW MESSAGE (example):
  The Model Report configuration contains an item having an unknown type 
  ("RplStatement"). This model report may have been created using a newer 
  version of RiverWare.

See change in Sim/ModelReportItem.cpp, method: okstat ModelReportItem::
addItemFromXMLElement(QDomElement).

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