merge upstream changes

diff --cc dygraph.js
index 724629a,37a9c30..4d086f7
--- 1/dygraph.js
--- 2/dygraph.js
+++ b/dygraph.js
@@@ -2005,7 -2006,7 +2012,7 @@@ Dygraph.prototype.parseArray_ = functio
      var parsedData = Dygraph.clone(data);
      for (var i = 0; i < data.length; i++) {
        if (parsedData[i].length == 0) {
--        this.error("Row " << (1 + i) << " of data is empty");
++        this.error("Row " + (1 + i) + " of data is empty");
          return null;
        }
        if (parsedData[i][0] == null