Fix vertical text misalignment on buttons on OS X

Fix as described here: http://successfulsoftware.net/2013/10/23/fixing-qt-4-for-mac-os-x-10-9-mavericks/

How official KeePassX 2.0 alpha 6 looks on OS X 10.9:
http://img-fotki.yandex.ru/get/6844/25698687.7/0_ce1d7_fe476d00_orig.png

And after the fix:
http://img-fotki.yandex.ru/get/4807/25698687.7/0_ce1d8_42c7075c_orig.png