fix($rootScope): ng-repeat can't handle NaN values. #4605

$watchCollection checks if oldValue !== newValue which does not work for NaN. This was causing
infinite digest errors, since comparing NaN to NaN in $watchCollection would always return false,
indicating that a change was occuring on each loop.

This fix adds a simple check to see if the current value and previous value are both NaN, and
if so, does not count it as a change.

Closes #4605

test/ng/rootScopeSpec.js

@@ -603,6 +603,10 @@ describe('Scope', function() {
           expect(log.empty()).toEqual([{newVal: [{}, []], oldVal: ['b', {}, []]}]);
         });
 
+        it('should not infinitely digest when current value is NaN', function() {
+          $rootScope.obj = [NaN];
+          $rootScope.$digest();
+        });
 
         it('should watch array-like objects like arrays', function () {
           var arrayLikelog = [];