New option localhost_only to restrict connections only to localhost

Bug-Debian: https://github.com/tats/w3m/issues/117

fm.h

@@ -836,6 +836,7 @@ global char AutoUncompress init(FALSE);
 global char PreserveTimestamp init(TRUE);
 global char ArgvIsURL init(TRUE);
 global char MetaRefresh init(FALSE);
+global char LocalhostOnly init(FALSE);
 
 global char fmInitialized init(FALSE);
 global char QuietMessage init(FALSE);

rc.c

@@ -223,6 +223,7 @@ static int OptionEncode = FALSE;
 #endif
 #define CMT_FOLLOW_REDIRECTION N_("Number of redirections to follow")
 #define CMT_META_REFRESH N_("Enable processing of meta-refresh tag")
+#define CMT_LOCALHOST_ONLY N_("Restrict connections only to localhost")
 
 #ifdef USE_MIGEMO
 #define CMT_USE_MIGEMO N_("Enable Migemo (Roma-ji search)")
@@ -698,6 +699,8 @@ struct param_ptr params9[] = {
      CMT_FOLLOW_REDIRECTION, NULL},
     {"meta_refresh", P_CHARINT, PI_ONOFF, (void *)&MetaRefresh,
      CMT_META_REFRESH, NULL},
+    {"localhost_only", P_CHARINT, PI_ONOFF, (void *)&LocalhostOnly,
+     CMT_LOCALHOST_ONLY, NULL},
 #ifdef INET6
     {"dns_order", P_INT, PI_SEL_C, (void *)&DNS_order, CMT_DNS_ORDER,
      (void *)dnsorders},

url.c

@@ -1696,6 +1696,10 @@ openURL(char *url, ParsedURL *pu, ParsedURL *current,
 	}
     }
 
+    if (LocalhostOnly && pu->host &&
+	strcasecmp(pu->host, "localhost") && strcasecmp(pu->host, "127.0.0.1"))
+	pu->host = NULL;
+
     uf.scheme = pu->scheme;
     uf.url = parsedURL2Str(pu)->ptr;
     pu->is_nocache = (option->flag & RG_NOCACHE);