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.

docs/tutorial/Makefile.am

@@ -37,7 +37,7 @@ EXTRA_DIST += \
 	images/tictactoe.png
 
 if HAVE_DOCBOOK
-html:
+html: gtk-tut.sgml
 	if test -w $(srcdir); then \
 	  (cd $(srcdir); \
 	   db2html gtk-tut.sgml; \
@@ -47,11 +47,13 @@ html:
 	   cp images/*.png html/images); \
 	fi
 
-pdf:
+pdf: gtk-tut.sgml
 	if test -w $(srcdir); then \
 	  (cd $(srcdir); db2pdf gtk-tut.sgml); \
 	fi
 
+all-local: html
+
 dist-hook: html
 	cp -Rp $(srcdir)/html $(distdir)
 else