doc: Allow selecting web site CSS style sheet in XSLT HTML build

doc/src/sgml/Makefile

@@ -258,6 +258,10 @@ postgres.xml: $(srcdir)/postgres.sgml $(ALMOSTALLSGML)
 	rm postgres.xmltmp
 # ' hello Emacs
 
+ifeq ($(STYLE),website)
+XSLTPROC_HTML_FLAGS += --param website.stylesheet 1
+endif
+
 xslthtml: xslthtml-stamp
 
 xslthtml-stamp: stylesheet.xsl postgres.xml

doc/src/sgml/stylesheet.xsl

@@ -10,7 +10,6 @@
 
 <!-- Parameters -->
 <xsl:param name="base.dir" select="'html/'"></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="make.valid.html" select="1"></xsl:param>
 <xsl:param name="generate.id.attributes" select="1"></xsl:param>
@@ -21,6 +20,15 @@
 <xsl:param name="chunk.quietly" select="1"></xsl:param>
 <xsl:param name="toc.max.depth">2</xsl:param>
 
+<xsl:param name="website.stylesheet" select="0"/>
+
+<xsl:param name="html.stylesheet">
+  <xsl:choose>
+    <xsl:when test="$website.stylesheet = 0">stylesheet.css</xsl:when>
+    <xsl:otherwise>http://www.postgresql.org/media/css/docs.css</xsl:otherwise>
+  </xsl:choose>
+</xsl:param>
+
 
 <!-- Change display of some elements -->