Replace UnicodeDecodeErrors raised during == and !=
compares of Unicode and other objects with a new
UnicodeWarning.

All other comparisons continue to raise exceptions.
Exceptions other than UnicodeDecodeErrors are also left
untouched.

This provides the proper warning for struct.pack().
PyErr_Warn() is now deprecated in favor of PyErr_WarnEx().
As mentioned by Tim Peters on python-dev.

 - Warn-raise ImportWarning when importing would have picked up a directory
   as package, if only it'd had an __init__.py. This swaps two tests (for
   case-ness and __init__-ness), but case-test is not really more expensive,
   and it's not in a speed-critical section.

 - Test for the new warning by importing a common non-package directory on
   sys.path: site-packages

 - In regrtest.py, silence warnings generated by the build-environment
   because Modules/ (which is added to sys.path for Setup-created modules)
   has 'zlib' and '_ctypes' directories without __init__.py's.

added message attribute compared to the previous version of Exception.  It is
also a new-style class, making all exceptions now new-style.  KeyboardInterrupt
and SystemExit inherit from BaseException directly.  String exceptions now
raise DeprecationWarning.

Applies patch 1104669, and closes bugs 1012952 and 518846.

  has already done the job.
* Use a macro form of PyErr_Occurred() inside the set_lookkey() function.

method still needs to support string exceptions, and allow None for the
third argument.  Documentation updates are needed, too.

happen in 2.3, but nobody noticed it still was getting generated (the
warning was disabled by default).  OverflowWarning and
PyExc_OverflowWarning should be removed for 2.5, and left notes all over
saying so.