increase decoder thread priority by 32 instead of 5; log errors

stepmania/src/arch/Sound/RageSoundDriver_CA.cpp

@@ -11,6 +11,7 @@
 #include "archutils/Unix/CrashHandler.h"
 #include <mach/thread_act.h>
 #include <mach/mach_init.h>
+#include <mach/mach_error.h>
 
 static AudioConverter *gConverter;
 
@@ -192,8 +193,10 @@ void RageSound_CA::SetupDecodingThread()
 {
 	/* Increase the scheduling precedence of the decoder thread. */
 	thread_precedence_policy po;
-	po.importance = 5;
-	thread_policy_set( mach_thread_self(), THREAD_PRECEDENCE_POLICY,
+	po.importance = 32;
+	kern_return_t ret = thread_policy_set( mach_thread_self(), THREAD_PRECEDENCE_POLICY,
                        (int *)&po, THREAD_PRECEDENCE_POLICY_COUNT );
+	if( ret != KERN_SUCCESS )
+		LOG->Warn( "thread_policy_set(THREAD_PRECEDENCE_POLICY) failed: %s", mach_error_string(ret) );
 }