[R6RS] comment #92 re-vote for and library rationale

[Matthew Flatt]

I finished the rationale for the library-specification compromise, and
placed it as the response to formal comment 92 (because that's the
lowest numbered of the relevant comments). I also put pointers in the
responses to 109, 110, 112, and 123 back to the response for 92.

I changed all the response votes for comment 92 from "A" to "A?". If
you approve of the rationale, change your "A?" back to an "A".

Matthew