Update pflua hash
bench.lua output tweaks

* src/bench.lua: Default to 50 iterations, and return results in MPPS.
Add graph generation targets

* src/Makefile (check-png-deps, graphs): Add targets for generating
  graphs from CSV files.
Use gettimeofday in bench.lua

* src/bench.lua: Use gettimeofday() as a high-resolution wall-clock
  timer.
Add ping-flood analysis

* src/Makefile: Add pflua-ping-flood.png target.
* src/ts/pcaps/igalia/ping-flood.pcap.tests: New expectations.
Tweak graph titles

* src/Makefile (pflua-1gb-1kb-tcp-port-5555.png): Tweak graph names.
Add portrange test to one-gigabyte tests

* deps/pflua: Update.
* src/ts/pcaps/igalia/one-gigabyte.pcap.tests: Add portrange test.