doc: Move htmlhelp output to subdirectory

This makes it behave more like the html output.  That will make some
subsequent changes across all output formats easier.

doc/src/sgml/Makefile

@@ -131,9 +131,13 @@ html-stamp: stylesheet.xsl postgres.sgml $(ALLSGML)
 	cp $(srcdir)/stylesheet.css html/
 	touch $@
 
-htmlhelp: stylesheet-hh.xsl postgres.sgml $(ALLSGML)
+htmlhelp: htmlhelp-stamp
+
+htmlhelp-stamp: stylesheet-hh.xsl postgres.sgml $(ALLSGML)
 	$(XMLLINT) $(XMLINCLUDE) --noout --valid $(word 2,$^)
 	$(XSLTPROC) $(XMLINCLUDE) $(XSLTPROCFLAGS) $(wordlist 1,2,$^)
+	cp $(srcdir)/stylesheet.css htmlhelp/
+	touch $@
 
 # single-page HTML
 postgres.html: stylesheet-html-nochunk.xsl postgres.sgml $(ALLSGML)
@@ -284,7 +288,7 @@ clean:
 # generated SGML files
 	rm -f $(GENERATED_SGML)
 # HTML Help
-	rm -f htmlhelp.hhp toc.hhc index.hhk
+	rm -rf htmlhelp/ htmlhelp-stamp
 # EPUB
 	rm -f postgres.epub
 # Texinfo

doc/src/sgml/stylesheet-hh.xsl

@@ -10,8 +10,10 @@
 <!-- Parameters -->
 <xsl:param name="htmlhelp.use.hhk" select="'1'"/>
 
+<xsl:param name="base.dir" select="'htmlhelp/'"></xsl:param>
 <xsl:param name="html.stylesheet" select="'stylesheet.css'"></xsl:param>
 <xsl:param name="use.id.as.filename" select="'1'"></xsl:param>
+<xsl:param name="manifest.in.base.dir" select="1"/>
 <xsl:param name="make.valid.html" select="1"></xsl:param>
 <xsl:param name="generate.id.attributes" select="1"></xsl:param>
 <xsl:param name="generate.legalnotice.link" select="1"></xsl:param>