docs: page.xsl: fix FAQ link in subdirectories

Links to the FAQ didn't work on pages in subdirectories, like
devhelp/libvirt-virterror.html or internals/command.html, because
they have had href_base prepended to them.

docs/page.xsl

@@ -54,7 +54,7 @@
             <xsl:when test="$pagename = a/@href">
               <span class="{$class}"><xsl:value-of select="a"/></span>
             </xsl:when>
-            <xsl:when test="a/@href = 'http://wiki.libvirt.org'">
+            <xsl:when test="starts-with(a/@href, 'http://wiki.libvirt.org')">
               <a title="{./span}" class="{$class}" href="{a/@href}"><xsl:value-of select="a"/></a>
             </xsl:when>
             <xsl:otherwise>