add IsShown() accessor which is sometimes more convenient than IsHidden()

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@57131 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/headercol.h

@@ -148,6 +148,8 @@ public:
         { ChangeFlag(wxCOL_HIDDEN, hidden); }
     virtual bool IsHidden() const
         { return HasFlag(wxCOL_HIDDEN); }
+    bool IsShown() const
+        { return !IsHidden(); }
 
     // for sortable columns indicate whether we should sort in ascending or
     // descending order

interface/wx/headercol.h

@@ -302,6 +302,13 @@ public:
      */
     virtual bool IsHidden() const;
 
+    /**
+        Returns @true if the column is currently shown.
+
+        This corresponds to the absence of wxCOL_HIDDEN flag.
+     */
+    bool IsShown() const;
+
     /**
         Sets the sort order for this column.