disallow automatic D2 minor when major is > 1 order of mag

looks confusing to have minor ticks 2,5,10,20,50, so drop to
just the orders of magnitude.
D1 is fine though, if you ask for that many minor ticks!

Author: alexcjohnson

src/plots/cartesian/axes.js

@@ -621,6 +621,10 @@ axes.prepMinorTicks = function(mockAx, ax, opts) {
                 } else {
                     mockAx.dtick = 'D1';
                 }
+            } else if(mockAx.dtick === 'D2' && +ax.dtick > 1) {
+                // the D2 log axis tick spacing is confusing for unlabeled minor ticks if
+                // the major dtick is more than one order of magnitude.
+                mockAx.dtick = 1;
             }
         }
         // put back the original range, to use to find the full set of minor ticks

test/jasmine/tests/axes_test.js

@@ -6628,6 +6628,27 @@ describe('Test axes', function() {
         });
 
         it('log auto - case 2', function(done) {
+            Plotly.newPlot(gd, {
+                data: [{
+                    x: [1, 10e10]
+                }],
+                layout: {
+                    width: 1000,
+                    xaxis: {
+                        type: 'log',
+                        minor: {
+                            showgrid: true
+                        }
+                    }
+                }
+            })
+            .then(function() {
+                _assert([ 1, 3, 5, 7, 9, 11 ]);
+            })
+            .then(done, done.fail);
+        });
+
+        it('log auto - case 3', function(done) {
             Plotly.newPlot(gd, {
                 data: [{
                     x: [1, 10e3]
@@ -6648,7 +6669,7 @@ describe('Test axes', function() {
             .then(done, done.fail);
         });
 
-        it('log auto - case 3', function(done) {
+        it('log auto - case 4', function(done) {
             Plotly.newPlot(gd, {
                 data: [{
                     x: [1, 10]
@@ -6669,7 +6690,7 @@ describe('Test axes', function() {
             .then(done, done.fail);
         });
 
-        it('log auto - case 4', function(done) {
+        it('log auto - case 5', function(done) {
             Plotly.newPlot(gd, {
                 data: [{
                     x: [1, 2]