Switch to C99 types (retaining compat with old compilers)

Seeing the "mpd_" prefix _everywhere_ is mind-numbing as the
mind needs to retrain itself to skip over the first 4 tokens of
a type to get to its meaning.  So avoid having extra characters
on my terminal to make it easier to follow code at 2:30 am in
the morning.

Please report any new issues you may come across on Free
toolchains.  I realize how difficult it can be to build/maintain
cross-compiling toolchains and I have no intention of forcing
people to upgrade their toolchains to build mpd.

Tested with gcc 2.95.4 and and gcc 4.3.1 on x86-32.

src/audioOutputs/audioOutput_alsa.c

@@ -214,7 +214,7 @@ configure_hw:
 		      snd_strerror(-err));
 		goto fail;
 	}
-	audioFormat->channels = (mpd_sint8)channels;
+	audioFormat->channels = (int8_t)channels;
 
 	err = snd_pcm_hw_params_set_rate_near(ad->pcmHandle, hwparams,
 					      &sampleRate, NULL);

src/audioOutputs/audioOutput_oss.c

@@ -482,9 +482,9 @@ static int oss_openDevice(void *data,
 	int ret;
 	OssData *od = data;
 
-	od->channels = (mpd_sint8)audioFormat->channels;
+	od->channels = (int8_t)audioFormat->channels;
 	od->sampleRate = audioFormat->sampleRate;
-	od->bits = (mpd_sint8)audioFormat->bits;
+	od->bits = (int8_t)audioFormat->bits;
 
 	if ((ret = oss_open(od)) < 0)
 		return ret;