spartan: make different blocks of annotated lines have different colors

mercurial/templates/spartan/map

@@ -55,7 +55,7 b' filelogentry = filelogentry.tmpl'
 # all table rows have equal height.
 annotateline = '
   <tr class="parity{parity}{ifeq(node, originalnode, ' thisrev')}">
-    <td class="annotate">
+    <td class="annotate parity{blockparity}">
       {if(blockhead,
           '<a href="{url|urlescape}annotate/{node|short}/{file|urlescape}{sessionvars%urlparameter}#l{targetline}">
              {rev}