We should start shipping a GLib 2.0-based version of libgda and gnome-db
(or at least prepare it) as soon as possible. So, the quickest way would be
to provide, in the file libgda/lib/gda-common/gda-common-defs.h #defines
for all the functions, macros, data types that are different for GObject
and GtkObject, and use these #define's everywhere so that the same source
code is used to compile both versions.

So, for example:

#if defined(HAVE_GOBJECT)
#  define gda_object_unref g_object_unref
#  define gda_object_ref g_object_ref
#  define GdaType GType
#else
#  define gda_object_unref gtk_object_unref
#  define gda_object_ref gtk_object_ref
#  define GdaType GtkType
#endif