title: DataGridView override top,left header cell click (select all)
body: <p>I want to override the behavior of a mouse click in the DataGridView header/column cell (top, left cell).  That cell causes all rows to be selected.  Instead, I want to stop it from selecting all rows.  I see an event for RowHeaderSelect and ColumnHeaderSelect but not one for that top, left header cell.</p>
  
  <p>Any ideas?  Am I just being blind?</p>