[docs] generator.throw() documentation inaccurate (issue 14911)

[yselivanov.ml at gmail.com]

http://bugs.python.org/review/14911/diff/10905/Doc/reference/expressions.rst
File Doc/reference/expressions.rst (right):

http://bugs.python.org/review/14911/diff/10905/Doc/reference/expressions.rst#newcode446
Doc/reference/expressions.rst:446: If provided, the ``tb`` argument is
used for the raised exception, otherwise
``traceback`` instead of ``tb``?

http://bugs.python.org/review/14911/