> The new io4.diff breaks test_io and test_univnewlines on Linux
oops, I missed this one.

Here is a new version: io5.diff, which should handle the "seen newlines"
better.

Two more bug fixes found by test_univnewlines: 
- write() should return the number of characters written, but before
they are newline-translated.
- a problem in tell(), my decoder can return two characters even when
you feed only one (example: decode(b'\r') holds the \r and returns
nothing. then a decode(b'x') returns both chars "\rx")