Merge commit 'refs/pr/965' into debian

#965

| add data index to legendFormatter data

| This adds the row index to the structure passed to the
| legendFormatter. Having the index enables quick indexing of external,
| unplotted auxiliary data for a point.

src/plugins/legend.js

@@ -201,6 +201,7 @@ Legend.generateLegendHTML = function(g, x, sel_points, oneEmWidth, row) {
   var data = {
     dygraph: g,
     x: x,
+    i: row,
     series: []
   };