Add a hint message about permissions if unable to get I/O permissions

for hardware OPL access.

Subversion-branch: /branches/opl-branch
Subversion-revision: 1844

opl/opl_linux.c

@@ -47,6 +47,14 @@ static int OPL_Linux_Init(unsigned int port_base)
     {
         fprintf(stderr, "Failed to get I/O port permissions for 0x%x: %s\n",
                         port_base, strerror(errno));
+
+        if (errno == EPERM)
+        {
+            fprintf(stderr,
+                    "\tYou may need to run the program as root in order\n"
+                    "\tto acquire I/O port permissions for OPL MIDI playback.\n");
+        }
+
         return 0;
     }