In case the user isn't allowed to access /dev/dsp or /dev/dsp isn't there

In case the user isn't allowed to access /dev/dsp or /dev/dsp isn't there
at all (my computer doesn't have a Sound Blaster), this doesn't mean
there's a bug in linuxaudiodev. The only error the test suite skips
is currently ImportError -- so that's what we raise. If you see a problem
with this patch, say so and I'll retract. If you think raising an ImportError
sucks, you're right -- but I ain't gonna buy a SB and I sure ain't gonna
let the test-suite fail on my machine.