Fixed the documented about buffer overflow error for "es#" and "et#" format
units.

* There was a link pointing to the section on the string.Formatter class (and
  multiple links in Python 3), when the section on the common format string
  syntax is probably more appropriate
* Fix references to various format() functions and methods
* Nested replacement fields may contain conversions and format specifiers,
  and this is tested in Python 3; see Issue #19729 for instance

Based on patches by Brian Brazil and Daniel Rocco.

Reported by Denis Akhiyarov on docs@

Fixed a crash when unpickle the functools.partial object with wrong state.
Fixed a leak in failed functools.partial constructor.
"args" and "keywords" attributes of functools.partial have now always types
tuple and dict correspondingly.

Based on patch by Aviv Palivoda.

Test test_wrong_cert() runs a server that rejects the client's certificate,
so ECONNRESET is reasonable in addition to SSLError. On the other hand, the
other three tests don't even need to run a server because they are just
testing the parsing of invalid certificate files.

This should fix intermittent failures on Windows where ECONNRESET was not
being caught.

Testing for a non-existing certificate file is already done in test_errors().
The wrongcert.pem test was originally testing behaviour with a mismatched
certificate.

Also add some more tests. Based on patch by Sye van der Veen.

functions: "s", "s*", "s#", "t#", "z", "z*", "z#", "w", "w*", "w#", "u",
"u#", "es", "et", "es#", "et#" and "c".

Augment htest to include all major IOBinding functions.

Reported by Mike Scalora on docs@p.o.

Issue #25907: Use {% trans %} tags in HTML templates to ease the translation of
the documentation. The tag comes from Jinja templating system, used by Sphinx.

Patch written by Julien Palard.

This was already done in the 3.5 branch; this just does the same in the 2.7
branch.

Issue #25843: When compiling code, don't merge constants if they are equal but
have a different types. For example, "f1, f2 = lambda: 1, lambda: 1.0" is now
correctly compiled to two different functions: f1() returns 1 (int) and f2()
returns 1.0 (int), even if 1 and 1.0 are equal.

Add a new _PyCode_ConstantKey() private function.

A single call to Pool.apply_async() will create only one process. To use all
of the pool's processes, it should be invoked multiple times:

    with Pool(processes=4) as pool:
        results = [pool.apply_async(func, ()) for i in range(4)]

Patch by Davin Potts.

This change helps to ignore text of PSF, BEOPEN.com and CNRI licenses when
translating the documentation. Patch written by Julien Palard who is
translating Python 3.5 doc to french. Text of other licenses already used
preformatted format.

Issue #24520: On FreeBSD, fpgetmask() was deprecated long time ago.
fedisableexcept() is now preferred.

non-UTF-8 encoding.

Originally added by Christian Heimes in 85ec2b5bfcd2.

Initial patch for the backport by Alecsandru Patrascu.

Debugging by Eryk Sun.