* configure.in: make xdelta not built by default, so poor users aren't confused

* libgimp/gimp.c
* app/blob.c
* app/errors.c
* plug-ins/script-fu/script-fu-server.c: fixes for glib changes with
s/g_debug/g_on_error_debug/ and s/g_vsprintf/g_strdup_vprintf/

-Yosh