Change ``set device'' so that it parses its arguments as one

Change ``set device'' so that it parses its arguments as one
device per argument rather than the old way of concatenating
everything then splitting the result at commas and whitespace.

Old syntax of ``set device /dev/cuaa0, /dev/cuaa1''
may no longer contain the comma, but syntax such as
``set device "!ssh host ppp -direct label"'' is now
possible.