[R6RS] non-opaque record equality

[Matthew Flatt]

Would it make sense for two records could be `equal?' when 

 1. they are instances of the same *non-opaque* record type, and 

 2. their corresponding field values are all `equal?'

? This change seems consistent with the SRFI's reflection support on
non-opaque records.

I have no strong opinion, but I thought I'd bring it up for a couple of
reasons: extending `equal?' this way has been convenient in MzScheme,
and I didn't see any discussion of this possibility in the R6RS or SRFI
email archives (but there was a lot of discussion specifically about
equality, and I could easily have overlooked specifics thoughts on
opacity).

Matthew