bug#22447: (rnrs hashtables): Mutation of immutable hashtable ignored

["Taylan Ulrich Bayırlı/Kammer"]

I couldn't find explicit wording in R6RS on what should happen, but I
would generally expect an attempt to mutate an immutable object to
raise an error.  In Guile,

    (hashtable-set! (hashtable-copy (make-eq-hashtable)) 'foo 'bar)

is silently ignored.

Taylan