Merge 30432:30436 from /nmap-exp/david/ipv6-ranges.

This is simple IPv6 unicast ranges. For example,
nmap -6 en.wikipedia.org/120 -sn

The other, more complicated part of this overall change is automatic
multicast scanning of large local subnets. That part isn't done yet.

nbase/nbase_str.c

@@ -93,6 +93,7 @@
 /* $Id$ */
 
 #include "nbase.h"
+#include <assert.h>
 #include <string.h>
 #include <stdarg.h>
 #include <stdio.h>
@@ -164,6 +165,18 @@ int Snprintf(char *s, size_t n, const char *fmt, ...)
 	return ret;
 }
 
+/* Make a new allocated null-terminated string from the bytes [start, end). */
+char *mkstr(const char *start, const char *end) {
+  char *s;
+
+  assert(end >= start);
+  s = (char *) safe_malloc(end - start + 1);
+  memcpy(s, start, end - start);
+  s[end - start] = '\0';
+
+  return s;
+}
+
 /* vsprintf into a dynamically allocated buffer, similar to asprintf in
    Glibc. Return the length of the buffer or -1 on error. */
 int alloc_vsprintf(char **strp, const char *fmt, va_list va) {