Apple on Thursday issued the first beta of Mac OS X 10.6.7, the  next security and maintenance update for its Snow Leopard operating  system, to developers for testing.   The first beta is dubbed Build 10J842 is a 338.6MB download in its delta  form. People familiar with the first beta said that its documentation  notes there are no known issues with the software.   Developers have reportedly been asked to focus on AirPort, Bonjour, SMB file sharing, and graphics drivers.   The first beta arrived just weeks   after Apple released Mac OS X 10.6.6 for Snow Leopard. That update  brought the Mac App Store, a new digital download destination to obtain  software for the Mac platform.   While it is unknown what new features or fixes might come in Mac OS X  10.6.7, the Mac App Store will likely prove to be the last major feature  added to Snow Leopard. Apple has already begun to hype   Mac OS X 10.7 Lion, its next major operating system release. Lion will  bring features from iOS, including a ...