Update the documentation about the Mac differences to indicate that the menu translation has different approaches on Carbon and Cocoa

Update the documentation about the Mac differences to indicate that the menu translation has different approaches on Carbon and Cocoa. Currently the documentation at http://doc.qt.nokia.com/4.7/mac-differences.html#translating-the-application-menu-and-native-dialogs is correct for Carbon. But for Cocoa the Qt translations need to be loaded in order to get the translations done.