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The version of the patch still makes a file an iterator but it no 
longer depends on xreadlines - it implements the readahead 
buffering inside the file object.

It is about 19% faster than xreadlines for normal text files and 
about 40% faster for files with 100k lines.

The methods readline and read do not use this readahead 
mechanism because it skews the current file position (just like 
xreadlines does).