Merging the py3k-pep3137 branch back into the py3k branch.

No detailed change log; just check out the change log for the py3k-pep3137
branch.  The most obvious changes:

  - str8 renamed to bytes (PyString at the C level);
  - bytes renamed to buffer (PyBytes at the C level);
  - PyString and PyUnicode are no longer compatible.

I.e. we now have an immutable bytes type and a mutable bytes type.

The behavior of PyString was modified quite a bit, to make it more
bytes-like.  Some changes are still on the to-do list.

Lib/test/regrtest.py

@@ -278,6 +278,9 @@ def main(tests=None, testdir=None, verbose=0, quiet=False, generate=False,
                 huntrleaks[1] = int(huntrleaks[1])
             if len(huntrleaks) == 2 or not huntrleaks[2]:
                 huntrleaks[2:] = ["reflog.txt"]
+            # Avoid false positives due to the character cache in
+            # stringobject.c filling slowly with random data
+            warm_char_cache()
         elif o in ('-M', '--memlimit'):
             test_support.set_memlimit(a)
         elif o in ('-u', '--use'):
@@ -357,9 +360,9 @@ def main(tests=None, testdir=None, verbose=0, quiet=False, generate=False,
 
     # Strip .py extensions.
     if args:
-        args = map(removepy, args)
+        args = list(map(removepy, args))
     if tests:
-        tests = map(removepy, tests)
+        tests = list(map(removepy, tests))
 
     stdtests = STDTESTS[:]
     nottests = NOTTESTS.copy()
@@ -768,6 +771,11 @@ def dash_R_cleanup(fs, ps, pic, abcs):
     # Collect cyclic trash.
     gc.collect()
 
+def warm_char_cache():
+    s = bytes(range(256))
+    for i in range(256):
+        s[i:i+1]
+
 def reportdiff(expected, output):
     import difflib
     print("*" * 70)