Fix angular-placeholder in IE9 when the input is required.

README.md

tests-always-included/angular-placeholder#6 (comment)

ie9RequiredFix.directive.js.coffee

angular.module('apruve.checkout.util').directive 'required', ->
  priority: 1
  restrict: 'A'
  require: '?ngModel'
  link: (scope, elm, attr, ctrl) ->
    return if !ctrl

    origRequired = ctrl.$validators.required
    ctrl.$validators.required = (modelValue, viewValue) ->
      return !(viewValue == attr.placeholder) and origRequired(modelValue, viewValue)
      
    attr.$observe 'required', ->
      ctrl.$validate()
    return