jqlite returns incorrect value for boolean attributes in some cases

[Narretz]

• Do you want to request a feature or report a bug?
  bug
• What is the current behavior?
  jqlite.attr(attrName) returns the lowercase version of attrName if the element has attrName set as a property. See the discussion in 'select' / 'ng-model' / 'ng-options' behaviour changed in 1.4.9 #14115
• What is the expected behavior?
  jqlite should always return the actual attribute value like jquery does.
• What is the motivation / use case for changing the behavior?
  mainly consistency with jquery, because this behavior doesn't seem to cause issues outside of tests.
• Which version of Angular, and which browser and OS does this issue affect? Did this work in previous
  versions of Angular? Please also test with the latest stable and snapshot versions.
  all versions up to 1.5.0

[mgol]

I'll do it as part of the other jQuery changes for 1.6.0.