Add -v0 to mean no output to stdout. Closes #265. Fixes #236.

CHANGELOG

@@ -1,5 +1,9 @@
 # Nmap Changelog ($Id$); -*-text-*-
 
+o When provided a verbosity of 0 (-v0), Nmap will not output any text to the
+  screen. This happens at the time of argument parsing, so the usual meaning of
+  "verbosity 0" is preserved. [isjing]
+
 o [Nsock] Avoid a crash on Windows and other systems which use nbase's
   vasprintf implementation. In the case of unknown OpenSSL errors,
   ERR_reason_error_string would return NULL, which could not be printed with

nmap.cc

@@ -1422,6 +1422,11 @@ void parse_options(int argc, char **argv) {
     case 'v':
       if (optarg && isdigit(optarg[0])) {
         o.verbose = atoi(optarg);
+        if (o.verbose == 0) {
+          o.nmap_stdout = fopen(DEVNULL, "w");
+          if (!o.nmap_stdout)
+            fatal("Could not assign %s to stdout for writing", DEVNULL);
+        }
       } else {
         const char *p;
         o.verbose++;