Existing links have been updated to use the new reST role.  In some
files, I have also made cosmetic changes to the header.

This update includes new entries that apply to 2.7 too, mention of class
decorators, mention of nonlocal, notes about bytecode, markup fixes and
some rewrappings.  Future backports of changes should be slightly
easier.

No change was necessary to make the file build, contrary to cporting.rst
that uses markup like :c:func: that needs to be changed to :cfunc: in
2.7.  Future backports should be straightforward.

Georg added this role in our 3.2 doc tools and gave the greenlight for a
backport on python-dev.

This code is a simplified version of the 3.2 code; the version of Sphinx
used with Python 2.7 doesn’t have the function used to parse markup like
:role:`text to be displayed <text to be processed>` (I was persuaded it
was a standard reST construct, but it is actually a Sphinx innovation
that has to be supported explicitly in role code —I’ll be damned).  It
is thus not possible to write for example :source:`the NEWS file
<Misc/NEWS>`, but :source:`Misc/NEWS` will work.

Confirm that the prime example is actually correct.  We get so many complaints about a "buggy example" on docs@python, let us hope this cuts them in half at least.

Fix closes issue12698 - make the no_proxy environment variable handling a bit lenient (accomodate spaces in between the items)

Fix closes Issue12183 - Explain the Symlink copy behavior in shutil.copytree. Patch by Petri Lehtinen.

This is a regression introduced in 9211a5d7d0b4, when uses of ST_MTIME
constants were changed to uses of st_mtime attributes.  As diagnosed in
the bug report, this change is not merely stylistic: st_mtime is a
float but ST_MTIME’s resolution is rounded to the seconds, so there was
a mismatch between the values seen by file_util and dep_util which
caused an sdist to be unnecessarily created a second time on an ext4
filesystem.

This patch has been tested by John S. Gruber, who reported the bug.
As this is a simple code revert, I think it’s okay to commit without a
unit test.

This prevents tests from failing when run from a Python installed in a
read-only directory.