Patch updated.

- SameFileError is now derived from EnvironmentError.
- Fixed documentation.
- Fixed test method name.

I investigated this patch:

- shutil.copyfile() and shutil.copy() raises SameFileError if source and destination are same file.

- shutil.move() never raises SameFileError. shutil.move() may raise exception if source and dest are same file, but it depends on underlying implementation of platform. Linux and Windows don't raise exception in this case.

- I am opposed to change shutil.move() to raise SameFileError, because such incompatible change can break existing applilcations.