kernel: bump to 3.10.29

firmware: Add max_clock_drift config.txt option to allow higher variations in audio timestamp before affecting clock
See: http://forum.xbmc.org/showthread.php?tid=185665&pid=1623383#pid1623383

firmware: Make the fifo timestamp mode conditional on timestamp period variance being lower than non-fifo mode
See: http://forum.stmlabs.com/showthread.php?tid=12535

userland: vcos: cleanup dummy threads properly
See: https://github.com/raspberrypi/userland/pull/141