DragonFly doesn't have the ossaudio library, so it won't build the oss
plugin. The PLIST was adjusted accordingly. Pkglint hated the Makefile
so it was cleaned up and a license entry (2-clause-bsd) was added.
pulseaudio plugin unless option selected. Option off by default
so no change to default package build.
Fixes build if you happen to have pulseaudio package installed when
building.
