Fixes #603724.

the terminal encoding on Windows and Unix.

Thanks to Skip Montanaro and Kalle Svensson for the patches.

For a file f, iter(f) now returns f (unless f is closed), and f.next()
is similar to f.readline() when EOF is not reached; however, f.next()
uses a readahead buffer that messes up the file position, so mixing
f.next() and f.readline() (or other methods) doesn't work right.
Calling f.seek() drops the readahead buffer, but other operations
don't.

The real purpose of this change is to reduce the confusion between
objects and their iterators.  By making a file its own iterator, it's
made clearer that using the iterator modifies the file object's state
(in particular the current position).

A nice side effect is that this speeds up "for line in f:" by not
having to use the xreadlines module.  The f.xreadlines() method is
still supported for backwards compatibility, though it is the same as
iter(f) now.

(I made some cosmetic changes to Oren's code, and added a test for
"file closed" to file_iternext() and file_iter().)

are disabled.

+ Continued looping until n bytes in the buffer have been filled, not
  just when n bytes have been read from the file.  This repairs the
  bug that f.readlines() only sucked up the first 8192 bytes of the file
  on Windows when universal newlines was enabled and f was opened in
  U mode (see Python-Dev -- this was the ultimate cause of the
  test_inspect.py failure).

+ Changed prototye to take a char* buffer (void* doesn't make much sense).

+ Squashed size_t vs int mismatches (in particular, besides the unsigned
  vs signed distinction, size_t may be larger than int).

+ Gets out under all error conditions now (it's possible for fread() to
  suffer an error even if it returns a number larger than 0 -- any
  "short read" is an error or EOF condition).

+ Rearranged and simplified declarations.

Highlights: import and friends will understand any of \r, \n and \r\n
as end of line. Python file input will do the same if you use mode 'U'.
Everything can be disabled by configuring with --without-universal-newlines.

See PEP278 for details.

const char* instead of char*.  The change is conceptually correct, and
indirectly fixes a compiler wng introduced when somebody else innocently
passed a const char* to this function.

Preliminary support.  What's here works, but needs fine-tuning.