bug#75721 patch from jonathan@tangential.ca.
MCAST_JOIN_GROUP/MCAST_LEAVE_GROUP socket option for the RFC 3678
support does not work on freebsd, using IP_ADD_MEMBERSHIP instead.
The multicast support in PHP 5.4 makes use of MCAST_JOIN_GROUP if it is present.
The problem is that OSX 10.7 added the constant, but did not correctly implement
the feature. This causes the setsockopt call to fail.
The solution to the problem is to not use MCAST_JOIN_GROUP on OSX.
For reference, this was also done in VLC:
* http://trac.videolan.org/vlc/ticket/6104#comment:19