enhacements for libao 0.8.6

it is mentioned in the TODO file of libao 0.8.6-1 (from debian sarge) that it is a "TODO" that libao do on the fly sample rate conversion. it would be nice that converted to 2 channels if number of channels is not supported by the sound card (e.g. my i810 only supports 2 channels) it would be useful that ao_open_live returned a detailed description of the error when failing, since now it only returns NULL and sends things like "libao - OSS cannot set channels to 1" to stderr. and also it would be nice a uniform method for selecting which sound card to use. say, sound card number n, with 0<=n. currently oss and alsa09 have different options for selecting sound card number and it needs a device name.