[R6RS] SRFIs for R6RS

[Anton van Straaten]

This looks good to me.  I agree with Kent that it would make sense to 
mention the withdrawal option, without committing to it.

It might also be worth including some language explaining why "the 
editors might decide to modify the specification".  Although this might 
be considered obvious, the more we can do to clarify the way in which we 
plan to use the SRFI process, the better.

A sentence like the following, adapted from Marc's message, ought to be 
sufficient: "Modification of the specification may occur due to other 
design constraints, such as design consistency with other features that 
are not under discussion as SRFIs."

Anton