If e.g. glib's configure detects that I have gtk-doc installed, but 
the SGML environment is not set up correctly, "make install" fails
due to the docs not being created.

Here is a simple fix for gtkdoc-mkhtml which will move the error from
installation time to build time to hopefully make it easier to find
the problem.

As an added bonus, it prevents the creation of the stamp file so that
restarting the build after fixing the SGML env will actually correct
the error.

--- gtkdoc-mkhtml.in.orig       Mon Dec  3 11:28:33 2001
+++ gtkdoc-mkhtml.in    Mon Dec  3 11:28:52 2001
@@ -24,7 +24,7 @@
       rm -f index.sgml
 fi
 
-jade -t sgml -w no-idref -d $gtkdocdir/gtk-doc.dsl $gtkdocdir/gtk-doc.dcl $2
+jade -t sgml -w no-idref -d $gtkdocdir/gtk-doc.dsl $gtkdocdir/gtk-doc.dcl $2 || exit 1
 sed s%href=\"%href=\"$module/% < index.sgml > index.sgml.tmp && mv index.sgml.tmp index.sgml
 
 echo "timestamp" > ../html.stamp