Fix segfault when opening pcap interface

When running corsaro with pcap interface as input corsaro flowtuple would attempt to read magic number from a corsaro file with mode other than binary (eg. trace file)
Merge pull request #7 from alepuccetti/fix_flowtuple_probe_magic

Fix segfault when opening pcap interface
fix ed_with_plugin macro on FreeBSD 10

for some reason FreeBSD 10 does not support the += syntax to append to a shell
variable.