fix(datepicker): Don't parse the date twice

Fixes angular-ui#3644, angular-ui#3617

Author: realityking

Diff for: src/datepicker/datepicker.js

@@ -650,7 +650,7 @@ function ($compile, $parse, $document, $position, dateFilter, dateParser, datepi
 
       // Detect changes in the view from the text box
       ngModel.$viewChangeListeners.push(function () {
-        scope.date = dateParser.parse(ngModel.$viewValue, dateFormat, scope.date) || new Date(ngModel.$viewValue);
+        scope.date = ngModel.$modelValue;
       });
 
       var documentClickBind = function(event) {