Added a command-line key generation tool. Currently builds and runs

on Linux, but the (very few) platform-specific bits are already
abstracted out of the main code, so it should port to other
platforms with a minimum of fuss.

[originally from svn r3762]

unix/.cvsignore

@@ -1,4 +1,4 @@
 Makefile.gtk Makefile
 local
-plink pterm putty puttytel psftp pscp
+plink pterm putty puttytel psftp pscp puttygen
 *.log

unix/uxcons.c

@@ -313,3 +313,8 @@ void frontend_keypress(void *handle)
      */
     return;
 }
+
+int is_interactive(void)
+{
+    return isatty(0);
+}

unix/uxgen.c

@@ -0,0 +1,36 @@
+/*
+ * uxgen.c: Unix implementation of get_heavy_noise() from cmdgen.c.
+ */
+
+#include <stdio.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#include "putty.h"
+
+char *get_random_data(int len)
+{
+    char *buf = snewn(len, char);
+    int fd;
+    int ngot, ret;
+
+    fd = open("/dev/random", O_RDONLY);
+    if (fd < 0) {
+	sfree(buf);
+	perror("puttygen: unable to open /dev/random");
+	return NULL;
+    }
+
+    ngot = 0;
+    while (ngot < len) {
+	ret = read(fd, buf+ngot, len-ngot);
+	if (ret < 0) {
+	    close(fd);
+	    perror("puttygen: unable to read /dev/random");
+	    return NULL;
+	}
+	ngot += ret;
+    }
+
+    return buf;
+}