Add a -c option (login shell command) with an error message. (from Edoardo Spadolini)

README

@@ -152,6 +152,7 @@ COMMANDLINE PARAMETERS
 ======================
 
  -a		Ignored.
+ -c		Shows error message and exits. (login shell command)
  -e		Ignored.
  -h		Ignored.
  -i user	Autologin and run the register -command hook for "user"
@@ -191,6 +192,7 @@ ERROR CODES
   11	Cannot run as root: Config file has shed_uid = 0
   12	Config file has an unrecognized token
   13	Config file: Negative value not accepted
+  15	dgamelaunch called with -c (login shell command); exited
   20	No menu defined, or no banner found for menu
   60	Cannot create a new terminal, or no termcap files.
   61	Cannot openpty()

dgamelaunch.c

@@ -2719,10 +2719,15 @@ main (int argc, char** argv)
 
   __progname = basename(strdup(argv[0]));
 
-  while ((c = getopt(argc, argv, "sqh:pi:aeW:SD")) != -1)
+  while ((c = getopt(argc, argv, "c:sqh:pi:aeW:SD")) != -1)
   {
     switch (c)
     {
+      case 'c':
+        fprintf(stderr, "This is not a shell account, you can't execute "
+                        "arbitrary commands.\n");
+        graceful_exit(15);
+        break;
       case 's':
 	showplayers = 1; break;