Before V4:
* API conventions overview and corrections
* GdaDataModel error codes
* review GdaDataModelAccess and error reporting

libgda/gda-meta-struct.c: gda_meta_struct_get_db_object() should use the same convention as _complement()
                          about case sensitiveness.

* All: add extra gpointer fields to class structures for future additions of signals

* GdaDataComparator::diff-computed

* a new GValue (with its specific type) to represent pseudo values such as "CURRENT_TIME", "CURRENT_DATE" and timestamp and maybe others
* restrict (control) the provider's exported symbols (normally limited to "plugin_*")





* _gda_tree_node_add_children(): last argument could steal the list instead of making a copy.