(Merge 3.3) Close #17702: On error, os.environb now removes suppress the except

context when raising a new KeyError with the original key.

diff --cc Lib/os.py
Simple merge

diff --cc Lib/test/test_os.py
Simple merge

diff --cc Misc/NEWS
index 7b62d16e07e269b34b8cb6e3bae7be3cfc7af071,81ad8f5d8fc958af2359fe090ff2df2db00e88d6..431674abbd5366e7d071a8232750cd488b9e7b47
--- 1/Misc/NEWS
--- 2/Misc/NEWS
+++ b/Misc/NEWS
@@@ -10,129 -12,10 +10,132 @@@ Projected Release date: 2013-09-0
  Core and Builtins
  -----------------
  
 +- Issue #18774: Remove last bits of GNU PTH thread code and thread_pth.h.
 +
 +- Issue #18771: Add optimization to set object lookups to reduce the cost
 +  of hash collisions.  The core idea is to inspect a second key/hash pair
 +  for each cache line retrieved.
 +
 +- Issue #16105: When a signal handler fails to write to the file descriptor
 +  registered with ``signal.set_wakeup_fd()``, report an exception instead
 +  of ignoring the error.
 +
 +- Issue #18722: Remove uses of the "register" keyword in C code.
 +
  - Issue #18667: Add missing "HAVE_FCHOWNAT" symbol to posix._have_functions.
  
 +- Issue #16499: Add command line option for isolated mode.
 +
 +- Issue #15301: Parsing fd, uid, and gid parameters for builtins
 +  in Modules/posixmodule.c is now far more robust.
 +
  - Issue #18368: PyOS_StdioReadline() no longer leaks memory when realloc()
 -  fails.
 +  fail.
 +
 +- Issue #17934: Add a clear() method to frame objects, to help clean up
 +  expensive details (local variables) and break reference cycles.
 +
 +Library
 +-------
 +
++- Issue #17702: On error, os.environb now removes suppress the except context
++  when raising a new KeyError with the original key.
++
 +- Issue #16809: Fixed some tkinter incompabilities with Tcl/Tk 8.6.
 +
 +- Issue #16809: Tkinter's splitlist() and split() methods now accept Tcl_Obj
 +  argument.
 +
 +- Issue #18324: set_payload now correctly handles binary input.  This also
 +  supersedes the previous fixes for #14360, #1717, and #16564.
 +
 +- Issue #18794: Add a fileno() method and a closed attribute to select.devpoll
 +  objects.
 +
 +- Issue #17119: Fixed integer overflows when processing large strings and tuples
 +  in the tkinter module.
 +
 +- Issue #18747: Re-seed OpenSSL's pseudo-random number generator after fork.
 +  A pthread_atfork() parent handler is used to seeded the PRNG with pid, time
 +  and some stack data.
 +
 +- Issue #8865: Concurrent invocation of select.poll.poll() now raises a
 +  RuntimeError exception.  Patch by Christian Schubert.
 +
 +- Issue #18777: The ssl module now uses the new CRYPTO_THREADID API of
 +  OpenSSL 1.0.0+ instead of the deprecated CRYPTO id callback function.
 +
 +- Issue #18768: Correct doc string of RAND_edg(). Patch by Vajrasky Kok.
 +
 +- Issue #18178: Fix ctypes on BSD. dlmalloc.c was compiled twice which broke
 +  malloc weak symbols.
 +
 +- Issue #18709: Fix CVE-2013-4238. The SSL module now handles NULL bytes
 +  inside subjectAltName correctly. Formerly the module has used OpenSSL's
 +  GENERAL_NAME_print() function to get the string represention of ASN.1
 +  strings for ``rfc822Name`` (email), ``dNSName`` (DNS) and
 +  ``uniformResourceIdentifier`` (URI).
 +
 +- Issue #18701: Remove support of old CPython versions (<3.0) from C code.
 +
 +- Issue #18756: Improve error reporting in os.urandom() when the failure
 +  is due to something else than /dev/urandom not existing (for example,
 +  exhausting the file descriptor limit).
 +
 +- Issue #18673: Add O_TMPFILE to os module. O_TMPFILE requires Linux kernel
 +  3.11 or newer. It's only defined on system with 3.11 uapi headers, too.
 +
 +- Issue #18532: Change the builtin hash algorithms' names to lower case names
 +  as promised by hashlib's documentation.
 +
 +- Issue #18405: Improve the entropy of crypt.mksalt().
 +
 +- Issue #12015: The tempfile module now uses a suffix of 8 random characters
 +  instead of 6, to reduce the risk of filename collision. The entropy was
 +  reduced when uppercase letters were removed from the charset used to generate
 +  random characters.
 +
 +- Issue #18585: Add :func:`textwrap.shorten` to collapse and truncate a
 +  piece of text to a given length.
 +
 +- Issue #18598: Tweak exception message for importlib.import_module() to
 +  include the module name when a key argument is missing.
 +
 +- Issue #18676: Change 'positive' to 'non-negative' in queue.py put and get
 +  docstrings and ValueError messages. Patch by Zhongyue Luo
 +
 +- Fix refcounting issue with extension types in tkinter.
 +
 +- Issue #8112: xlmrpc.server's DocXMLRPCServer server no longer raises an error
 +  if methods have annotations; it now correctly displays the annotations.
 +
 +- Issue #18600: Added policy argument to email.message.Message.as_string,
 +  and as_bytes and __bytes__ methods to Message.
 +
 +- Issue #18671: Output more information when logging exceptions occur.
 +
 +- Issue #18621: Prevent the site module's patched builtins from keeping
 +  too many references alive for too long.
 +
 +- Issue #4885: Add weakref support to mmap objects.  Patch by Valerie Lambert.
 +
 +- Issue #8860: Fixed rounding in timedelta constructor.
 +
 +Tests
 +-----
 +
 +- Issue #18792: Use "127.0.0.1" or "::1" instead of "localhost" as much as
 +  possible, since "localhost" goes through a DNS lookup under recent Windows
 +  versions.
 +
 +
 +What's New in Python 3.4.0 Alpha 1?
 +===================================
 +
 +Release date: 2013-08-03
 +
 +Core and Builtins
 +-----------------
  
  - Issue #16741: Fix an error reporting in int().