logging: warn() methods and function to be deprecated.

[Vinay Sajip]

In response to an issue (#13235) raised on the Python bug tracker, I'm going to
deprecate the warn() methods in the Logger and LoggerAdapter classes in the
stdlib logging package, as well the module-level warn() function.

The warn() variants were synonyms for the warning() methods and function, and a
holdover from before the time that logging was added to Python.They were not
documented; it's probably time to retire them, so I've added a
DeprecationWarning to appear in 3.3, and they'll be completely removed in 3.4
(along with the WARN synonym for WARNING). With this change, all the logging
levels are adjectives which apply to the logged message: DEBUG, INFO, WARNING,
ERROR and CRITICAL.

I don't believe the WARN/warn variants were used much, if at all - but this is
just a heads up for anyone who might have used them.

Regards,

Vinay Sajip