Make sure that sane-desc is compiled when generating HTML pages.

doc/Makefile.in

@@ -174,6 +174,9 @@ html-man: $(MANPAGES)
 	  cat $${page} | $(MAN2HTML) > $${page}.html; \
 	done
 
+../tools/sane-desc:
+	cd ../tools ; $(MAKE) sane-desc
+
 sane-backends.html: $(wildcard descriptions/*.desc) ../tools/sane-desc
 	@../tools/sane-desc -m html-backends-split -s descriptions \
 	 -i "The following table summarizes the backends/drivers distributed \