Use ATOMIC-INCF in NEXT-CLASS-HASH-VALUE.
Use ATOMIC-INCF in NEXT-CLASS-HASH-VALUE.

Not replacing every use of %ATOMIC-FIXNUM-ADD-SYMBOL with it yet
because that requires declaiming the symbols as fixnums. That has
bootstrapping issues as PROCLAIM tries to check the types.

froggey/Mezzano,froggey/Mezzano