configure.ac.in: fix missing XDT_I18N call
glib's gettext machinery wasn't set up correctly, on make run getting the error:
/usr/bin/msgfmt: error while opening "@MSGFMT_OPTS@" for reading: No such file or directory
Closes: #234 (closed) Signed-off-by: Enrico Weigelt, metux IT consult info@metux.net