Remove atomicfile class. The interface provided by opener(atomic=True) is inherently unsafe: if an exception is raised in the code using the atomic file, the possibly incomplete file will be renamed to its final destination, defeating the whole purpose of atomic files. To get around this, we would either need some bad hacks involving sys.exc_info (to make sure things work in except: blocks), or an interface to say "file is complete; rename it". This is the exact interface provided by atomictempfile. Since there are no remaining users of the atomicfile class, just remove it.

adding he
llo
abort: '\n' and '\r' disallowed in filenames
adding he
llo
abort: '\n' and '\r' disallowed in filenames
adding hell
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abort: '\n' and '\r' disallowed in filenames
adding hell
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abort: '\n' and '\r' disallowed in filenames
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