title: Selectively Allow Editing of XamDataGrid Cell
body: <p>I've got a situation where I have set the DataSource of a XamDataGrid to a list of ViewModels.  Thus, my XamDataGrid is expected to have multiple rows.  I would like to bind the editablity of a given cell to a property on the cell's viewmodel.  My initial idea is just to bind the Field's AllowEdit property to the ViewModel (which would make sense to anyone except Infragistics), but that doesn't work.  How can I accomplish this?</p>
  
  <p>I would like to accomplish this through bindings, if at all possible.</p>