mbuffer: Update to version 20140310 from 20091227

The previous version of mbuffer could not be built out-of-tree and
seems rather old [1].

[1] http://www.maier-komor.de/mbuffer.html



Signed-off-by: Ash Charles <ashcharles@gmail.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>