Silly multicast propagation fix: exclude upstream sender to never send duplicate multicasts back to where they came from
0.2.3 - OSX bug fix, multicast propagation fix, no incompatible protocol changes
Further increase verbosity of TRACE messages for duplicate multicasts
Several things:

(1) Probable fix for issue #7 and major cleanup of EthernetTap code with consolidation for all unix-like systems and specialization for different flavors only when needed.

(2) Refactor of Buffer<> to make its members private, and Packet to use Buffer's methods exclusively to access them. This improves clarity and means we're no longer lying about Buffer's role in the code's security posture.

(3) Add -fstack-protect to Makefile to bounds check stack variables.
Small compiler warning fix
Enable -fstack-protector on Linux too