fix(input[radio]): use non-strict comparison for checkedness

This was introduced during the switch to ESLint (b1bc251#diff-c244afd8def7f268b16ee91a0341c4b2R1691), 
but it is a breaking change. In master, we made an exception
for this comparison when we introduced jshint eqeqeq (which was not
backported to 1.5.x).

PR (#15289)

src/ng/directive/input.js

@@ -1753,7 +1753,9 @@ function radioInputType(scope, element, attr, ctrl) {
 
   ctrl.$render = function() {
     var value = attr.value;
-    element[0].checked = (value === ctrl.$viewValue);
+    // We generally use strict comparison. This is behavior we cannot change without a BC.
+    // eslint-disable-next-line eqeqeq
+    element[0].checked = (value == ctrl.$viewValue);
   };
 
   attr.$observe('value', ctrl.$render);

test/ng/directive/inputSpec.js

@@ -3871,6 +3871,17 @@ describe('input', function() {
     });
 
 
+    it('should use non-strict comparison between model and value', function() {
+      $rootScope.selected = false;
+      var inputElm = helper.compileInput('<input type="radio" ng-model="selected" ng-value="false">' +
+                   '<input type="radio" ng-model="selected" ng-value="\'\'">' +
+                   '<input type="radio" ng-model="selected" ng-value="0">');
+
+      expect(inputElm[0].checked).toBe(true);
+      expect(inputElm[1].checked).toBe(true);
+      expect(inputElm[2].checked).toBe(true);
+    });
+
     it('should watch the expression', function() {
       var inputElm = helper.compileInput('<input type="radio" ng-model="selected" ng-value="value">');