Merge branch 'PR723'

This merges changes by @kbaggott in danvk/dygraphs PR #723,
to allow points to be selected (and thus legends to show up)
on touchscreens.

diff --cc src/dygraph-interaction-model.js
index 494b638,411aae4..4fd33d9
--- 1/src/dygraph-interaction-model.js
--- 2/src/dygraph-interaction-model.js
+++ b/src/dygraph-interaction-model.js
@@@ -472,9 -473,12 +474,12 @@@ DygraphInteraction.startTouch = functio
  /**
   * @private
   */
 -Dygraph.Interaction.moveTouch = function(event, g, context) {
 +DygraphInteraction.moveTouch = function(event, g, context) {
    // If the tap moves, then it's definitely not part of a double-tap.
    context.startTimeForDoubleTapMs = null;
+  
+  // clear the last touch if it's doing something else
+   context.lastTouch = null;
  
    var i, touches = [];
    for (i = 0; i < event.touches.length; i++) {

diff --cc src/dygraph-utils.js
index c0b8f34,63be1d1..54b6b69
--- 1/src/dygraph-utils.js
--- 2/src/dygraph-utils.js
+++ b/src/dygraph-utils.js
@@@ -198,7 -192,8 +198,8 @@@ export function findPos(obj) 
   * @return {number}
   * @private
   */
 -Dygraph.pageX = function(e) {
 +export function pageX(e) {
+   if (e.isTouchOver) return (!e.changedTouches[0] || e.changedTouches[0].pageX < 0) ? 0 : e.changedTouches[0].pageX;
    return (!e.pageX || e.pageX < 0) ? 0 : e.pageX;
  };
  
@@@ -210,7 -205,8 +211,8 @@@
   * @return {number}
   * @private
   */
 -Dygraph.pageY = function(e) {
 +export function pageY(e) {
+   if (e.isTouchOver) return (!e.changedTouches[0] || e.changedTouches[0].pageY < 0) ? 0 : e.changedTouches[0].pageY;
    return (!e.pageY || e.pageY < 0) ? 0 : e.pageY;
  };