user-manual: run xsltproc without --nonet option

The --nonet option prevents xsltproc from going to the network to find
anything.  But it always tries to find them locally first, so for a
user with the necessary docbook stylesheets installed the build will
work just fine without xsltproc attempting to use the network; all
--nonet does is make it fail rather than falling back on that.  That
doesn't seem particularly helpful.

Signed-off-by: "J. Bruce Fields" <bfields@citi.umich.edu>

Documentation/Makefile

@@ -106,7 +106,7 @@ 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
+XSLTOPTS = --xinclude --stringparam html.stylesheet docbook-xsl.css
 
 user-manual.html: user-manual.xml
 	xsltproc $(XSLTOPTS) -o $@ $(XSLT) $<