Update autogen.sh
Update autogen.sh

Make autogen.sh test for the location of the current directory, and
warn if the checkout is not complete.

If gtk-doc is not installed (for instance, on an embedded minimal
set up), do not fail and just provide a stub gtk-doc.make.

ebassi/json-glib,ebassi/json-glib,Distrotech/json-glib,frida/json-glib,Distrotech/json-glib,Distrotech/json-glib,GNOME/json-glib,brauliobo/json-glib,robtaylor/json-glib-gvariant,frida/json-glib,oerdnj/json-glib,GNOME/json-glib,oerdnj/json-glib,brauliobo/json-glib,oerdnj/json-glib,brauliobo/json-glib,oerdnj/json-glib,robtaylor/json-glib-gvariant,ebassi/json-glib