fix bug in heatmap + non-heatmap hover

if you make this plot, you could never hover on the scatter points:
Plotly.newPlot(gd, [
    {x:[1,2,3], y: [1,4,7], z:[[1,2,3],[4,5,6],[7,8,9]], type:'heatmap'},
    {x:[1,2,3], y:[1,4,7]}
],{hovermode:'closest'})
Fx.MAXDIST had moved so sorting point distance was broken with heatmaps.

Author: alexcjohnson

src/traces/heatmap/hover.js

@@ -10,12 +10,13 @@
 'use strict';
 
 var Fx = require('../../plots/cartesian/graph_interact');
+var constants = require('../../plots/cartesian/constants');
 var Lib = require('../../lib');
 
 
 module.exports = function hoverPoints(pointData, xval, yval, hovermode, contour) {
     // never let a heatmap override another type as closest point
-    if(pointData.distance < Fx.MAXDIST) return;
+    if(pointData.distance < constants.MAXDIST) return;
 
     var cd0 = pointData.cd[0],
         trace = cd0.trace,
@@ -46,8 +47,8 @@ module.exports = function hoverPoints(pointData, xval, yval, hovermode, contour)
             return;
         }
     }
-    else if(Fx.inbox(xval - x[0], xval - x[x.length - 1]) > Fx.MAXDIST ||
-            Fx.inbox(yval - y[0], yval - y[y.length - 1]) > Fx.MAXDIST) {
+    else if(Fx.inbox(xval - x[0], xval - x[x.length - 1]) > constants.MAXDIST ||
+            Fx.inbox(yval - y[0], yval - y[y.length - 1]) > constants.MAXDIST) {
         return;
     }
     else {
@@ -99,7 +100,7 @@ module.exports = function hoverPoints(pointData, xval, yval, hovermode, contour)
     return [Lib.extendFlat(pointData, {
         index: [ny, nx],
         // never let a 2D override 1D type as closest point
-        distance: Fx.MAXDIST + 10,
+        distance: constants.MAXDIST + 10,
         x0: x0,
         x1: x1,
         y0: y0,

src/traces/scatter/hover.js

@@ -11,6 +11,7 @@
 
 var Lib = require('../../lib');
 var Fx = require('../../plots/cartesian/graph_interact');
+var constants = require('../../plots/cartesian/constants');
 var ErrorBars = require('../../components/errorbars');
 var getTraceColor = require('./get_trace_color');
 var Color = require('../../components/color');
@@ -59,7 +60,7 @@ module.exports = function hoverPoints(pointData, xval, yval, hovermode) {
 
             Lib.extendFlat(pointData, {
                 // never let a 2D override 1D type as closest point
-                distance: Fx.MAXDIST + 10,
+                distance: constants.MAXDIST + 10,
                 x0: x0,
                 x1: x1,
                 y0: y0,