osx: fix interface selection for ipv4 multicast joins
osx: fix install

Use POSIX compliant -R parameter instead of obsolete -r.
On linux they are equivalent, on OS X -r is not supported.
build: download dvbscan files even if linuxdvb is disabled
Merge pull request #403 from dmarion/osx

osx: fix interface selection for ipv4 multicast joins