Add examples for open’s new opener argument

[storchaka_gmail.com]

http://bugs.python.org/review/13424/diff/6494/Doc/library/functions.rst
File Doc/library/functions.rst (right):

http://bugs.python.org/review/13424/diff/6494/Doc/library/functions.rst#newco...
Doc/library/functions.rst:938: The following example is an alternative
implementation for opening files
I doubt that an alternative implementation is a good usage example.  First, this
violates the "one obvious way" principle.  Second, this does not justify the
adding of the new parameter to already complicated open(), because you can do
this without it.

http://bugs.python.org/review/13424/diff/6494/Doc/library/functions.rst#newco...
Doc/library/functions.rst:959: ...     dir_fd = os.open(dirname, os.O_RDONLY)
Here is a file descriptor leak.

[eric.araujo]

http://bugs.python.org/review/13424/diff/6494/Doc/library/functions.rst
File Doc/library/functions.rst (right):

http://bugs.python.org/review/13424/diff/6494/Doc/library/functions.rst#newco...
Doc/library/functions.rst:938: The following example is an alternative
implementation for opening files
This was an easy idea for an example, and I thought it could be easily map to
some windows API for readers.

http://bugs.python.org/review/13424/diff/6494/Doc/library/functions.rst#newco...
Doc/library/functions.rst:959: ...     dir_fd = os.open(dirname, os.O_RDONLY)
Oops!  I noticed the unclosed file objects in the first example (and judged they
were okay here) but did not catch this one.