Slot Viewer Fix: Showing/Hiding Priority was forcing Cnt column to be shown.
Bug Number: n/a
Release notes (y/n): no
For Release Nums: 7.2

Some additional processing required for the Slot Viewer's support for the 
Red/Gray "X" icon buttons in slot display columns was causing the "Series 
Display Compression" mode's "Cnt" column to be shown.  (This had been 
resolvable by turning on, and then turning off Series Display Compression).

The following pair of methods was augmented with a parameter to record and 
re-apply a list of hidden columns.

   void SlotDataTableModel::recordSlotCol_colWidthMap (
      QMap<SlotColRef,int>& colWidthMap,
      QList<int>& hiddenColList,
      const QList<SlotColRef>* limitToSlots) const;

   void SlotDataTableModel::applySlotCol_colWidthMap (
      QMap<SlotColRef,int>& colWidthMap,
      const QList<int>& hiddenColList,
      bool fitMissingCols);

This new provision (list of hidden columns) is used in this method:
   SlotDataTableView::recreateHorizontalHeaderView();

The relevant call to that method was in method SlotQtDlg::cellLayoutRecomputed()
where special processing for the Slot Viewer is determined with use of this 
method: bool SlotDataTableView::closeButtonsSupported().

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