entry-view: fix rb_entry_view_scroll_to_iter with gtk 3.14

Since scrolling the tree view is now animated, the row visibility checks in
gtk_tree_view_set_cursor don't work when it's called immediately after
gtk_tree_view_scroll_to_cell - so it scrolls again, and picks a target point
that leaves the selected row at the top or bottom of the view rather than the
middle.  Instead of gtk_tree_view_set_cursor, just select the row by
manipulating the GtkTreeSelection.