bar: fix normalised group bar plots

* Fixed bug computing the normalisation of bar plots in group mode.

* The bug was caused by calling `sieve.put` with bar sizes that didn't
  take into account the bar base.

* Bar plots in stack and relative mode weren't affected by this bug,
  because traces that set a bar base are excluded from the
  stack/relative mode.

Author: n-riesco

src/traces/bar/set_positions.js

@@ -503,8 +503,8 @@ function stackBars(gd, sa, sieve) {
             if(!isNumeric(bar.s)) continue;
 
             // stack current bar and get previous sum
-            var barBase = sieve.put(bar.p, bar.s),
-                barTop = barBase + bar.s;
+            var barBase = sieve.put(bar.p, bar.b + bar.s),
+                barTop = barBase + bar.b + bar.s;
 
             // store the bar base and top in each calcdata item
             bar.b = barBase;
@@ -537,7 +537,7 @@ function sieveBars(gd, sa, sieve) {
         for(var j = 0; j < trace.length; j++) {
             var bar = trace[j];
 
-            if(isNumeric(bar.s)) sieve.put(bar.p, bar.s);
+            if(isNumeric(bar.s)) sieve.put(bar.p, bar.b + bar.s);
         }
     }
 }

test/jasmine/tests/bar_test.js

@@ -543,6 +543,27 @@ describe('Bar.setPositions', function() {
         assertPointField(cd, 'y', [[0.75, 0.50, 0.25], [0.25, 0.50, 0.75]]);
     });
 
+    it('should honor barnorm (group+base case)', function() {
+        var gd = mockBarPlot([{
+            base: [3, 2, 1],
+            y: [0, 0, 0]
+        }, {
+            y: [1, 2, 3]
+        }], {
+            bargap: 0,
+            barmode: 'group',
+            barnorm: 'fraction'
+        });
+
+        expect(gd._fullLayout.barnorm).toBe('fraction');
+
+        var cd = gd.calcdata;
+        assertPointField(cd, 'b', [[0.75, 0.50, 0.25], [0, 0, 0]]);
+        assertPointField(cd, 's', [[0, 0, 0], [0.25, 0.50, 0.75]]);
+        assertPointField(cd, 'x', [[-0.25, 0.75, 1.75], [0.25, 1.25, 2.25]]);
+        assertPointField(cd, 'y', [[0.75, 0.50, 0.25], [0.25, 0.50, 0.75]]);
+    });
+
     it('should honor barnorm (stack case)', function() {
         var gd = mockBarPlot([{
             y: [3, 2, 1]