user-manual: ensure generated manual references stylesheet

The generated user manual is rather hard to read thanks to the lack of
the css that's supposed to be included from docbook-xsl.css.

I'm totally ignorant of the toolchain; grubbing through xmlto and
related scripts, the easiest way I could find to ensure that the
generated html links to the stylesheet is by calling xsltproc directly.
Maybe there's some better way.

Signed-off-by: "J. Bruce Fields" <bfields@citi.umich.edu>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/Makefile

@@ -105,8 +105,11 @@ clean:
 user-manual.xml: user-manual.txt user-manual.conf
 	$(ASCIIDOC) -b docbook -d book $<
 
+XSLT = http://docbook.sourceforge.net/release/xsl/current/html/docbook.xsl
+XSLTOPTS = --nonet --xinclude --stringparam html.stylesheet docbook-xsl.css
+
 user-manual.html: user-manual.xml
-	xmlto html-nochunks $<
+	xsltproc $(XSLTOPTS) -o $@ $(XSLT) $<
 
 glossary.html : glossary.txt sort_glossary.pl
 	cat $< | \