main.c, fix stdout and stderr redirection and buffering with regard to '-o' and '-p'

in response to a bug report from  Johann Glaser
  "#259 Pipe mode: buffering"
  http://sourceforge.net/p/ngspice/bugs/259/

src/main.c

@@ -939,8 +939,8 @@ main(int argc, char **argv)
 
             case 'o':       /* Output file */
               if (optarg) {
-                  /* turn off buffering for stdout */
-                  setbuf(stdout, NULL);
+                  /* switch to line buffering for stdout */
+                  setvbuf(stdout, NULL, _IOLBF, BUFSIZ);
                   sprintf (log_file, "%s", optarg);
                   orflag = TRUE;
               }
@@ -950,6 +950,8 @@ main(int argc, char **argv)
               iflag = TRUE;
               istty = TRUE;
               ft_pipemode = TRUE;
+              /* switch to line buffering for stdout */
+              setvbuf(stdout, NULL, _IOLBF, BUFSIZ);
               break;
 
             case 'q':       /* Command completion */
@@ -1013,11 +1015,13 @@ main(int argc, char **argv)
         }
 //        oflag = TRUE; /* All further output to -o log file */
 #else
-        /* Connect stdout to file log_file and log stdout */
+        /* Connect stdout and stderr to file log_file and log stdout */
         if (!freopen (log_file, "w", stdout)) {
             perror (log_file);
             sp_shutdown (EXIT_BAD);
         }
+        dup2(fileno(stdout), fileno(stderr));
+        setvbuf(stdout, NULL, _IOLBF, BUFSIZ); /* enable line buffering */
 #endif
     } /* orflag */