again, this is almost completely untested, unix only, and i'm mainly looking for comments on the interface (both the extended socket options interface and the APR_SO_MC_REUSEADDR idea).
Looks good on cursory review.
As a nitpick, why not APR_SO_EXT_GROUP_JOIN and apr_socket_join_arg_t instead? Realizing, of course, APR_SO_MC_REUSEADDR needs the MC to avoid the collision (and has the implicit REUSEPORT if available), but do we really have to propagate that MC_ elsewhere? I'm ambivalent on it, but the mc_'s sort of strike me funny. Not a big deal either way... -- justin
