Issue #4237: io.FileIO() was raising invalid warnings caused by insufficient initialization of PyFileIOObject struct members.

does not return an iterator for the 4th and 5th items.
(sequence-like and mapping-like state)

A list is not an iterator...

Will backport to 2.6 and 2.5.

closefd=True is the only accepted value with a file name.

order to actually test what it was supposed to test, i.e. that the code
in the __del__ method did not crash.  Use instead the new helper
test_support.captured_output().

Turn them into unit tests, and correct an obvious typo:
    (("a", "b") ("c", "d") ("e", "f"))
compiles even with the missing commas, but does not execute very well...