Migrate all Python scripts to Python 3.

Most of them are now _mandatory_ P3 scripts, because I'm tired of
maintaining everything to be compatible with both versions.

The current exceptions are gdb.py (which has to live with whatever gdb
gives it), and kh2reg.py (which is actually designed for other people
to use, and some of them might still be stuck on P2 for the moment).

contrib/make1305.py

@@ -1,9 +1,11 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 import sys
 import string
 from collections import namedtuple
 
+assert sys.version_info[:2] >= (3,0), "This is Python 3 code"
+
 class Multiprecision(object):
     def __init__(self, target, minval, maxval, words):
         self.target = target
@@ -89,21 +91,21 @@ class Multiprecision(object):
         for i in range(nwords):
             srcpos = i * self.target.bits + start
             maxbits = min(self.target.bits, start + bits - srcpos)
-            wordindex = srcpos / self.target.bits
+            wordindex = srcpos // self.target.bits
             if srcpos % self.target.bits == 0:
-                word = self.getword(srcpos / self.target.bits)
+                word = self.getword(srcpos // self.target.bits)
             elif (wordindex+1 >= len(self.words) or
                   srcpos % self.target.bits + maxbits < self.target.bits):
                 word = self.target.new_value(
                     "(%%s) >> %d" % (srcpos % self.target.bits),
-                    self.getword(srcpos / self.target.bits))
+                    self.getword(srcpos // self.target.bits))
             else:
                 word = self.target.new_value(
                     "((%%s) >> %d) | ((%%s) << %d)" % (
                         srcpos % self.target.bits,
                         self.target.bits - (srcpos % self.target.bits)),
-                    self.getword(srcpos / self.target.bits),
-                    self.getword(srcpos / self.target.bits + 1))
+                    self.getword(srcpos // self.target.bits),
+                    self.getword(srcpos // self.target.bits + 1))
             if maxbits < self.target.bits and maxbits < bits:
                 word = self.target.new_value(
                     "(%%s) & ((((BignumInt)1) << %d)-1)" % maxbits,
@@ -127,11 +129,11 @@ class CodegenTarget(object):
         self.valindex = 0
         self.stmts = []
         self.generators = {}
-        self.bv_words = (130 + self.bits - 1) / self.bits
+        self.bv_words = (130 + self.bits - 1) // self.bits
         self.carry_index = 0
 
     def nwords(self, maxval):
-        return (maxval.bit_length() + self.bits - 1) / self.bits
+        return (maxval.bit_length() + self.bits - 1) // self.bits
 
     def stmt(self, stmt, needed=False):
         index = len(self.stmts)
@@ -149,7 +151,7 @@ class CodegenTarget(object):
         return name
 
     def bigval_input(self, name, bits):
-        words = (bits + self.bits - 1) / self.bits
+        words = (bits + self.bits - 1) // self.bits
         # Expect not to require an entire extra word
         assert words == self.bv_words