Changed the way we open the dsp to prevent deadlock if another program

opens the dsp between plugin_test() and plugin_open().  Now we always
open it with O_NONBLOCK and remove the blocking later if needed.  The
ALSA docs claim that this is required by the OSS spec, but that is
not so obvious.


git-svn-id: http://svn.xiph.org/trunk/ao@1756 0101bb08-14d6-0310-b084-bc0e0c8e3800