[patch] libao generates mangled error messages when verbosity=0

I've been noticing a cryptic error message emanating from programs I've been writing:

%" in channel matrix "%"

I tracked this down to libao. When verbosity is nonzero, a (somewhat) more meaningful error message appears:

ao_pulse ERROR: Unrecognized channel name "%" in channel matrix "%"

The code that generates this message does so partly using aerror() (which checks the verbosity level before printing) and partly using fprintf() (which doesn't).

Attached is a patch to only use aerror().