timesequence mod: bring gnuplot arrows in foreground

Larger graphs show many sequncenumber graphs as well as ack graphs. These lines will hide data-retransmission graphs - this should not be the case. Just bring ACK and SACK info to foreground.

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
core: format print_usage()

Just some tidy coding style cleanups

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>