In daemon mode, send error messages to parent to write them on stderr.

This allows to get a better error message than "Spawning the daemon failed."
when initialization fails.

The error message is sent through the pipe. When init is OK, just send
a null byte.

common.c

@@ -34,6 +34,7 @@
 #include <openssl/bio.h>
 #include <openssl/buffer.h>
 #include "common.h"
+#include "daemon.h"
 
 shairport_cfg config;
 
@@ -41,10 +42,16 @@ int debuglev = 0;
 
 void die(char *format, ...) {
     fprintf(stderr, "FATAL: ");
+    
     va_list args;
     va_start(args, format);
+
     vfprintf(stderr, format, args);
+    if (config.daemonise)
+        daemon_fail(format, args); // Send error message to parent
+    
     va_end(args);
+    
     fprintf(stderr, "\n");
     shairport_shutdown();
 }