Added comment about VS 2008 and PGO builds.

- Factor out the duplication of EHLO/HELO in login() and sendmail() to
  a new function, ehlo_or_helo_if_needed().
- Use ehlo_or_helo_if_needed() in starttls()
- Check for the starttls exception in starttls() in the same way as
  login() checks for the auth extension.
Contributed by Bill Fenner.

Fixes issue 829951 - http://bugs.python.org/issue829951

compliance with PEP 3118.

to work with the newest Sphinx.

are used in a Structure or Union constructor.

passed to a Structure or Union constructor.

that array types do not live longer than needed.

Not sure if these are the correct values, but save_stdout has to be set before its usage...

Refactor if/elif chain for clarity and speed.  Remove dependency on subclasses having to implement _empty and _full.

exec call and when creating a recursive instance.

The duplication is intentional -- this paragraph is in a section
describing additions to the sys module, and there's a later section
that mentions the switch.  I think most people scan the what's-new and
don't read it in detail, so a bit of duplication is OK.

precision. This has been discussed at http://bugs.python.org/issue1682. It's
useful primarily for teaching, but it also demonstrates how to implement a
member of the numeric tower, including fallbacks for mixed-mode arithmetic.

I expect to write a couple more patches in this area:
 * Rational.from_decimal()
 * Rational.trim/approximate() (maybe with different names)
 * Maybe remove the parentheses from Rational.__str__()
 * Maybe rename one of the Rational classes
 * Maybe make Rational('3/2') work.

empty() and full().