Display Confirmation Message on GridView Deleting

ref : http://codeasp.net/articles/asp-net/48/display-confirmation-message-on-gridview-deleting
ref : http://www.codeproject.com/KB/webforms/GridViewConfirmDelete.aspx
ref : http://www.asp.net/data-access/tutorials/adding-client-side-confirmation-when-deleting-cs