[issue4016] improve linecache: reuse tokenize.detect_encoding() and io.open()

[STINNER Victor]

STINNER Victor <victor.stinner at haypocalc.com> added the comment:

It was easy to remove the itertools dependency: only itertools.chain() 
was really used and a simple "for ...: yield" is enough to get the 
same behaviour (test_tokenize.py runs fine). With the new version of 
the patch, the bootstrap works correctly.

Added file: http://bugs.python.org/file12333/linecache_refactor-2.patch

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