Add a special case code to deal with unexpected large files.

# On a Linux with large file support (LFS) using a Python without LFS,
# stat() will raise EOVERFLOW.  This unambiguously indicates that the
# file exists because it only occurs when the size of the file can't
# find into the stat struct.

This change is only needed for Python 2.1, because LFS is
automatically configured starting with Python 2.2.