Add i18n support

This will be needed to get better error messages to
users of the D-Bus API. We use glib's builtin gettext
support. No strings marked as translatable yet, we'll
need to mark those user-visible strings carefully and
review them.

autogen.sh

@@ -1,5 +1,7 @@
 #!/bin/sh
 aclocal || exit 1
+autoheader || exit 1
+glib-gettextize -f -c || exit 1
 autoconf || exit 1
 automake -a -c || exit 1
 ./configure $*