Try increasing compression buffer size.

This is in response to an error like:

2013-04-08T23:58:59.619+0000 lumberjack_wait_for_ack: waiting for ack
2013-04-08T23:58:59.619+0000 lumberjack_wait_for_ack: received ack: 98304
Assertion failed proto.c:381 in lumberjack_flush(), insist(rc == 0): compress2(..., 16402, ..., 25983) failed; returned -5
Aborted
Guard buf not being NULL-terminated.