[liblo] patch for multicast support

[Stephen S. <rad...@gm...>]

Hello,

Here is a patch against the current svn (revision 89) to add support
for multicast groups to LibLo.

For sending, it adds a "ttl" variable to the lo_address structure, and
uses setsockopt() to set it before sendto() is called.

For receiving, it adds a new protocol ID called "LO_UDP_MC".  This is
0xA, so it both corresponds with LO_UDP and also adds new bit flag.

I changed all references to LO_UDP to use & instead of ==.  This is
necessary because, when setting up the server, setsockopt() must be
called between socket creation and the call to bind() in order to
allow port reuse.  (Required for multicast.)

Please see this page for a nice description of multicast:
http://ntrg.cs.tcd.ie/undergrad/4ba2/multicast/antony/index.html

I've previously added multicast support to Pd's OSC objects, with
which I've tested these modifications.  In my group we're using
multicast along with OSC quite a lot in order to have different
programs on the local network share information on a single "bus".

Please consider adding this patch to LibLo!  Comments are welcome.

Thanks,
Steve