Sets the current sort column to be sort_column_id
.
The this will resort itself to reflect this change, after emitting a `GtkTreeSortable:
GtkTreeSortable:sort-column-changed
` signal. sort_column_id
may either be a regular column id, or one of the
following special values:
this |
A `GtkTreeSortable` |
sort_column_id |
the sort column id to set |
order |
The sort order of the column |