Teach vvp about -N

Added support for the -N option, which causes $stop and ^C to behave
like $finish with an exit code of 1.

While I was at it, I noticed that the summary line in the man page for
vvp was missing a couple of options, so I fixed that.

vvp/main.cc

@@ -207,6 +207,7 @@ int main(int argc, char*argv[])
       FILE *logfile = 0x0;
       extern void vpi_set_vlog_info(int, char**);
       extern bool stop_is_finish;
+      extern int  stop_is_finish_exit_code;
 
 #ifdef __MINGW32__
 	/* In the Windows world, we get the first module path
@@ -225,7 +226,7 @@ int main(int argc, char*argv[])
         /* For non-interactive runs we do not want to run the interactive
          * debugger, so make $stop just execute a $finish. */
       stop_is_finish = false;
-      while ((opt = getopt(argc, argv, "+hl:M:m:nsvV")) != EOF) switch (opt) {
+      while ((opt = getopt(argc, argv, "+hl:M:m:nNsvV")) != EOF) switch (opt) {
          case 'h':
            fprintf(stderr,
                    "Usage: vvp [options] input-file [+plusargs...]\n"
@@ -236,6 +237,7 @@ int main(int argc, char*argv[])
 		   " -M -           Clear VPI module path\n"
                    " -m module      Load vpi module.\n"
 		   " -n             Non-interactive ($stop = $finish).\n"
+                   " -N             Same as -n, but exit code is 1 instead of 0\n"
 		   " -s             $stop right away.\n"
                    " -v             Verbose progress messages.\n"
                    " -V             Print the version information.\n" );
@@ -257,6 +259,10 @@ int main(int argc, char*argv[])
 	  case 'n':
 	    stop_is_finish = true;
 	    break;
+          case 'N':
+            stop_is_finish = true;
+            stop_is_finish_exit_code = 1;
+            break;
 	  case 's':
 	    schedule_stop(0);
 	    break;

vvp/stop.cc

@@ -44,6 +44,7 @@
 
 struct __vpiScope*stop_current_scope = 0;
 bool stop_is_finish;  /* When set, $stop acts like $finish (set in main.cc). */
+int  stop_is_finish_exit_code = 0;
 
 #ifndef USE_READLINE
 static char* readline_stub(const char*prompt)
@@ -490,6 +491,7 @@ void stop_handler(int rc)
         /* The user may be running in a non-interactive environment, so
          * they want $stop and <Control-C> to be the same as $finish. */
       if (stop_is_finish) {
+           vpip_set_return_value(stop_is_finish_exit_code);
 	    schedule_finish(0);
 	    return;
       }

vvp/vvp.man

@@ -4,7 +4,7 @@ vvp - Icarus Verilog vvp runtime engine
 
 .SH SYNOPSIS
 .B vvp
-[-sv] [-Mpath] [-mmodule] [-llogfile] inputfile [extended-args...]
+[-nNsvV] [-Mpath] [-mmodule] [-llogfile] inputfile [extended-args...]
 
 .SH DESCRIPTION
 .PP
@@ -46,6 +46,11 @@ This flag makes $stop or a <Control-C> a synonym for $finish.
 It can be used to give the program a more meaningful interface when
 running in a non-interactive environment.
 .TP 8
+.B -N
+This flag does the same thing as -n, but results in an exit code
+of 1 if the stimulation calls $stop.  It can be used to indicate a
+simulation failure when running a testbench.
+.TP 8
 .B -s
 Stop. This will cause the simulation to stop in the beginning, before
 any events are scheduled. This allows the interactive user to get