QLineEdit's clear button is half-resolution on Retina displays

In Qt 5.2, QLineEdit was given the new clearButtonEnabled property. On Macs that support Retina resolution, the clear button icon appears at half resolution.

Steps to reproduce

1. Use a Mac with a Retina display
2. In Qt Creator, create a new Qt Widgets Application
3. Open MainWindow.ui
4. Add a QLineEdit
5. Turn on clearButtonEnabled
6. Observe that the pixels of the clear button icon are twice the size of the pixels of the text and widget border (see attached screenshot)