Add support for wxDV_NO_HEADER to OS X/Cocoa wxDataViewCtrl.

Also use this flag with the tree control in the sample to test it and also
because it doesn't make much sense to have a single column without title
anyhow.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62601 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/osx/cocoa/dataview.h

@@ -502,6 +502,8 @@ public:
     id GetItemAtRow(int row) const;
 
 private:
+    void InitOutlineView(long style);
+
     wxCocoaOutlineDataSource* m_DataSource;
 
     wxCocoaOutlineView* m_OutlineView;