Fix typo.
Add benchmark binary.
Hopefully speed up packet capture.
Fix up benchmark.

Turns out that benchmarking from a live interface is silly, because it's always
blocked on the interface, not on the actual code.  Switched to benchmarking from
a file, which produces much more repeatable results.
Modify packet capture a bit to for speed.

Used benchmark to test this out.

Old:
(/tmp/bench is tools/benchmark with the old code)
gconnell@zombie-test1.mtv:/$ /tmp/bench -file /tmp/foo
Took 3.334896s to process 1000000 packets, 3.334us per packet, 0 nil packets
gconnell@zombie-test1.mtv:/$ /tmp/bench -file /tmp/foo
Took 3.329675s to process 1000000 packets, 3.329us per packet, 0 nil packets

New:
(/tmp/bench2 is tools/benchmark with the new code)
gconnell@zombie-test1.mtv:/$ /tmp/bench2 -file /tmp/foo
Took 1.588695s to process 1000000 packets, 1.588us per packet, 0 nil packets
gconnell@zombie-test1.mtv:/$ /tmp/bench2 -file /tmp/foo
Took 1.580306s to process 1000000 packets, 1.58us per packet, 0 nil packets

About a 50% reduction in the initial packet copy.  This seemed to work pretty
repeatably.
Merge branch 'speedcopy' of github.com:gconnell/gopcap into speedcopy

Conflicts:
	pcap.go
Merge pull request #20 from gconnell/speedcopy

Speedcopy