In 1.9, Kernel.open calls to_open on its argument if it supports that 
method.  The to_open method is supposed to return an open IO stream, I 
suppose.

I wonder why open doesn't use the to_io conversion instead.  If I want 
to write a stream-like object, I have to implement to_io and to_open, 
and chances are they will do the same thing. What is the benefit to have 
these as separate conversions?

	David