Inspired by a pattern in NoMachine's NX.  Consistently zeroed buffers
compress better with ssh and friends.  Note that you'll need to rebuild
all your protocol libraries to take advantage of this.
Signed-off-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Jeremy Huddleston <jeremyhu@apple.com>
Reviewed-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Backported-to-NX-by: Ulrich Sibiller <uli42@gmx.de>