Mac-specific: Update libao library to version 1.2.2

maclibs/include/ao/ao.h

@@ -126,7 +126,7 @@ int              ao_driver_id(const char *short_name);
 int      ao_default_driver_id(void);
 ao_info       *ao_driver_info(int driver_id);
 ao_info **ao_driver_info_list(int *driver_count);
-char       *ao_file_extension(int driver_id);
+const char *ao_file_extension(int driver_id);
 
 /* miscellaneous */
 int          ao_is_big_endian(void);

maclibs/include/ao/plugin.h

@@ -42,7 +42,7 @@ int ao_plugin_play(ao_device *device, const char *output_samples,
 		uint_32 num_bytes);
 int ao_plugin_close(ao_device *device);
 void ao_plugin_device_clear(ao_device *device);
-char *ao_plugin_file_extension();
+const char *ao_plugin_file_extension();
 
 #ifdef __cplusplus
 }