Actually build the tutorial if enabled
Actually build the tutorial if enabled

Previously we required an explicit "make html" in this subdirectory
for no reason.  Just build it if make is invoked at the toplevel
and we have docbook.

Distrotech/gtk,Distrotech/gtk,Unity-Technologies/gtk,Unity-Technologies/gtk,Unity-Technologies/gtk,Distrotech/gtk,johne53/MB3Gtk-2,johne53/MB3Gtk-2,Distrotech/gtk,Unity-Technologies/gtk,Unity-Technologies/gtk,johne53/MB3Gtk-2,Distrotech/gtk,johne53/MB3Gtk-2,johne53/MB3Gtk-2