possible to, for example, use MacOS-partitioned hard disks and removable
media under B2/Unix even if the OS doesn't understand Mac partition maps
by specifying the appropriate block device name as a Mac volume
- fixed typo in audio_dummy.cpp
- added minimally required UDP tunneling code to ether_dummy.cpp
- main_unix.cpp: if pthreads are not supported, we trigger the Ethernet
interrupt in the 60Hz ticker; this makes UDP tunneling work under
NetBSD/m68k (as the only form of networking)