Fix for ticket #570: Interactive prompting is always active.

Control prompting with variable "interactive" and stop setting it by default.
Add code in main.c to set it for an interactve session.

src/frontend/control.c

@@ -227,7 +227,8 @@ docommand(wordlist *wlist)
         {
             int nargs = wl_length(wlist->wl_next);
             if (nargs < command->co_minargs) {
-                if (command->co_argfn) {
+                if (command->co_argfn &&
+                    cp_getvar("interactive", CP_BOOL, NULL, 0)) {
                     command->co_argfn (wlist->wl_next, command);
                 } else {
                     fprintf(cp_err, "%s: too few args.\n", s);

src/main.c

@@ -1091,6 +1091,13 @@ int main(int argc, char **argv)
         cp_nocc = FALSE;
     }
 
+    if ((iflag || istty) && !ft_batchmode) {
+        /* Enable interactive prompting. */
+
+        bool x_true = TRUE;
+        cp_vset("interactive", CP_BOOL, &x_true);
+    }
+
     if (ft_servermode) {             /* in server no init file */
         readinit = FALSE;
     }

src/spinit.in

@@ -12,7 +12,6 @@ set x11lineararcs
 ** set the number of threads in openmp
 ** default (if compiled with --enable-openmp) is: 2
 *set num_threads=4
-set interactive
 
 strcmp __flag $program "ngspice"
 if $__flag = 0