BUG: PIL Image array interface has the wrong size for YCbCr

Reported at <http://python.6.n6.nabble.com/PIL-Image-array-interface-has-the-wrong-size-for-YCbCr-td2103100.html>
Patch at <https://bitbucket.org/effbot/pil-2009-raclette/commits/e4a3b2e608b5a71cf23c0393d0d7bd4dd7900d7d>