Finished script that writes the pkts sent
[minor] Edit comment
Adapted example to most recent results

This code has to be double-checked though.
Improved script

Made a constant into a variable, and added a line to output the file
with the aggregate result needed by the overhead plugin.
Added unit test to script; refactoring

Taken out the responsibility of computing the average number of packets
sent by the source (see packets-sent.sh). The overhead.py plugin can be
executed not as a standalone program for unit testing.
Refactor of (was-) sz.sh

The script was born out of an emergency, so it was a mess, starting with
a close-to-meaningless name. Substituted hard-coded names with
variables, so it is easier to adapt it to new results when we have them.
Improved the debug mode, so the main script won't be executed if in
debug mode (symlinks will be created though).
Fixed problem with basicBitrate