Fixed some nit-picking bugs in GtkCellArea

Fixed some nit-picking bugs in GtkCellArea

  - Dont try fetching a cell renderer for an event when the event
    coordinate is outside the cell area allocation (can happen
    on the y axis, not all events are button events).
  - Dont remove focus-line-width (inner area) an extra time from
    GtkCellArea->event
  - Dont remove focus-line-width from the cell area at all for the
    editable widget... use the whole area including the focus line
    (compared with git master behaviour and now it looks right, check
    the multiline editable string in testtreeedit).