If you are run the uname system call from a program that is emulating
linux, for example, it should return "linux" -- not netbsd -- as the os.

Perhaps we want a program, emul, that takes two args, a system to
emulate and a command line:
	emul linux command args
This would then look in /emul/linux along the "path" for command and run
it.  (i.e. prefix /emul/linux to each component of $path and do a stat
and then exec the program/shell it finds.)