Fix outline color on CCLabelTTF

Without this, the outline would always be black.

Tested on devices running iOS 6.1.3 and 7.0.6. Shadows with different color/offset works, as does the outline width (it seems NSAttributedString doesn't explicitly set line width, like it does with the foreground color). shadowBlurRadius does work.

Note: This is a resubmission of pull request #636 which was closed during the apocalypse.