Fix for issue with UDP multicast socket on OSX.

Previously I was unable to bind multiple listeners to the same multicast
socket as OSX seems to require SO_REUSEPORT option to also be set on the
socket.

Resolves #2937.
Merge pull request #2939 from tsungg/bugfix-osxudp-multicast

Fix for issue with UDP multicast socket on OSX.
ofxGui: fix bugs in last commit
update CHANGELOG
ofFbo: fix min/max filters settings