xsl/calendar-summary: skip events older than 1 year

should speed up build process by much

xsl/calendar-summary.xsl

@@ -29,6 +29,9 @@
   <xsl:template match="event">
     <xsl:param name="link"/>
 
+    <!-- Events must have started at least one year ago -->
+    <xsl:variable name="minstart" select="date:add(date:date-time(), '-P366D')"/>
+    <xsl:if test="starts-with(date:difference(start, $minstart), '-')">
       <event>
 	<title>
 	  <xsl:choose>
@@ -59,6 +62,7 @@
 	</link>
 	<!-- TODO: Link -->
       </event>
+    </xsl:if>
   </xsl:template>
 
 </xsl:stylesheet>