Mac/Retina: Fix painting of "Details" button

For example in the projects mode

Task-number: QTCREATORBUG-10917
Change-Id: Ic6bcc10f9794451101d56b1871b37768641bac35
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>