Tell gviz what date format we like to use.

Otherwise it rewrites our dates into "Nov 11, 2012 1:02 PM" format.  12-hour
time is misleading, so let's discourage it.
diff --git a/render.js b/render.js
index 3d3ba34..2fcc0a6 100644
--- a/render.js
+++ b/render.js
@@ -904,6 +904,20 @@
       t = new google.visualization.Table(el);
       datatable = dataToGvizTable(grid);
     }
+    var dateformat = new google.visualization.DateFormat({
+      pattern: 'yyyy-MM-dd'
+    });
+    var datetimeformat = new google.visualization.DateFormat({
+      pattern: 'yyyy-MM-dd HH:mm:ss'
+    });
+    for (var coli = 0; coli < grid.types.length; coli++) {
+      console.debug('doing dateformat for', coli);
+      if (grid.types[coli] === T_DATE) {
+	dateformat.format(datatable, coli);
+      } else if (grid.types[coli] === T_DATETIME) {
+	datetimeformat.format(datatable, coli);
+      }
+    }
   });
   
   enqueue(chartops ? 'chart=' + chartops : 'view', function() {