When calling clutter_model_iter_next () / clutter_model_iter_prev () we need
to update the row for the iterator. In order to improve the peformance of
iterating this change adds a private row mutator and switches ClutterListModel
to use it.
* clutter/clutter-model-default.c:
(clutter_model_default_new),
(clutter_model_default_newv): Move the constructors in the
right file
* clutter/clutter-model-private.h: Add a private header for
the ClutterModel implementations
* clutter/clutter-model.c:
(clutter_model_check_type),
(clutter_model_set_n_columns),
(clutter_model_set_column_type): Mark as private to Clutter,
not static to ClutterModel
* clutter/Makefile.am: Add clutter-model-private.h
