merge in upstream changes

diff --cc dygraph-canvas.js
Simple merge

diff --cc dygraph.js
index 497c7c5,89a461f..23d2bcc
--- 1/dygraph.js
--- 2/dygraph.js
+++ b/dygraph.js
@@@ -1451,6 -1457,8 +1456,8 @@@ Dygraph.dateTicker = function(startDate
   * Add ticks when the x axis has numbers on it (instead of dates)
   * @param {Number} startDate Start of the date window (millis since epoch)
   * @param {Number} endDate End of the date window (millis since epoch)
 - * @param {function} formatter: Optional formatter to use for each tick value
+  * @param self
++ * @param {function} attribute accessor function.
   * @return {Array.<Object>} Array of {label, value} tuples.
   * @public
   */
@@@ -1653,12 -1661,11 +1666,12 @@@ Dygraph.prototype.drawGraph_ = function
        this.boundaryIds_[i-1] = [0, series.length-1];
      }
  
 -    var extremes = this.extremeValues_(series);
 -    var thisMinY = extremes[0];
 -    var thisMaxY = extremes[1];
 +    var seriesExtremes = this.extremeValues_(series);
 +    extremes[seriesName] = seriesExtremes;
 +    var thisMinY = seriesExtremes[0];
 +    var thisMaxY = seriesExtremes[1];
-     if (minY === null || thisMinY < minY) minY = thisMinY;
-     if (maxY === null || thisMaxY > maxY) maxY = thisMaxY;
+     if (minY === null || (thisMinY != null && thisMinY < minY)) minY = thisMinY;
+     if (maxY === null || (thisMaxY != null && thisMaxY > maxY)) maxY = thisMaxY;
  
      if (bars) {
        for (var j=0; j<series.length; j++) {