Build the HTML manual; add the HTML & PDF to the distribution; install them.

* doc/manual/Makefile.am (dist_html_DATA, dist_pdf_DATA): New variables.
  (manual.html): New target.
  (manual.pdf): Use $(DBLATEX), uppercase.

* configure.ac: Check for `xsltproc'.  Add `--with-docbook-xsl' option.

doc/manual/Makefile.am

@@ -7,9 +7,22 @@ dblatex_opts = \
  -P doc.collab.show=0 \
  -P latex.output.revhistory=0
 
+# Include the manual in the tarball.
+dist_html_DATA = manual.html
+dist_pdf_DATA = manual.pdf
+
+manual.html: $(DOCBOOK_FILES)
+	if test "$(XSLTPROC)" != ""; then				\
+		$(XSLTPROC) --nonet --xinclude --output manual.html	\
+	 	   $(docbookxsl)/html/docbook.xsl manual.xml;		\
+	else								\
+		@echo "Please install xsltproc and rerun configure.";	\
+		exit 1;							\
+	fi
+
 manual.pdf : $(DOCBOOK_FILES)
-	if test "$(dblatex)" != ""; then \
-	        $(dblatex) $(dblatex_opts) manual.xml; \
+	if test "$(DBLATEX)" != ""; then \
+	        $(DBLATEX) $(dblatex_opts) manual.xml; \
 	else \
 	        echo "Please install dblatex and rerun configure."; \
 	        exit 1; \