Allow the device name to be passed to linuxaudiodev.open(), for

Allow the device name to be passed to linuxaudiodev.open(), for
consistency with the built-in open() (and every other sane open()
function, for that matter).  The two valid ways to call this open() are
now open(mode) and open(device, mode).

For backwards compatibility, retain the old open(mode) calling syntax --
this makes the error message when you call open(device) a bit confusing,
but oh well.

This is the first half of SF patch #644977.