Log Message:
Changes 2.7.13:
Core and Builtins
-----------------
- Issue 28847: dumbdbm no longer writes the index file in when it is not
  changed and supports reading read-only files.
- Issue 11145: Fixed miscellaneous issues with C-style formatting of types
  with custom __oct__ and __hex__.
- Issue 24469: Fixed memory leak caused by int subclasses without overridden
  tp_free (e.g. C-inherited Cython classes).
- Issue 19398: Extra slash no longer added to sys.path components in case of
  empty compile-time PYTHONPATH components.
- Issue 21720: Improve exception message when the type of fromlist is unicode.
  fromlist parameter of __import__() only accepts str in Python 2 and this
  will help to identify the problem especially when the unicode_literals
  future import is used.
- Issue 26906: Resolving special methods of uninitialized type now causes
  implicit initialization of the type instead of a fail.
- Issue 18287: PyType_Ready() now checks that tp_name is not NULL.
  Original patch by Niklas Koep.
- Issue 24098: Fixed possible crash when AST is changed in process of
  compiling it.
- Issue 28350: String constants with null character no longer interned.
- Issue 27942: String constants now interned recursively in tuples and frozensets.
- Issue 15578: Correctly incref the parent module while importing.
- Issue 26307: The profile-opt build now applies PGO to the built-in modules.
- Issue 26020: set literal evaluation order did not match documented behaviour.
- Issue 27870: A left shift of zero by a large integer no longer attempts
  to allocate large amounts of memory.
- Issue 25604: Fix a minor bug in integer true division; this bug could
  potentially have caused off-by-one-ulp results on platforms with
  unreliable ldexp implementations.
- Issue 27473: Fixed possible integer overflow in str, unicode and bytearray
  concatenations and repetitions.  Based on patch by Xiang Zhang.
- Issue 27507: Add integer overflow check in bytearray.extend().  Patch by
  Xiang Zhang.
- Issue 27581: Don't rely on wrapping for overflow check in
  PySequence_Tuple().  Patch by Xiang Zhang.
- Issue 23908: os functions, open() and the io.FileIO constructor now reject
  unicode paths with embedded null character on Windows instead of silently
  truncating them.
- Issue 27514: Make having too many statically nested blocks a SyntaxError
  instead of SystemError.