fix thinko in GetOutput size calculation when count_diff>=4096 where
size must be 16384 (full buffer, 4*4096) not 4096: fixes stuttering
output with especially openal with high sample rates. fix the signed-
unsigned comparison warnings in oss code. fix broken playback if user
passes a rate option>65535 (just reject invalid rate values.) fix or
revise several driver messages. print error messages to stderr. kill
shutdown_output(), move its tiny functionality to drivers' shutdown
procs. remove the unnecessary output_result>0 check before sending
audio data to driver (we already break out of the loop if res<=0 a
few lines above that.) several other cleanups which I simply forgot
what they were about..