New instructions load-f64, load-u64

* libguile/instructions.c (FOR_EACH_INSTRUCTION_WORD_TYPE): Add word
  types for immediate f64 and u64 values.
  (TYPE_WIDTH): Bump up by a bit, now that we have 32 word types.
  (NOP, parse_instruction): Use 64-bit meta type.

* libguile/vm-engine.c (load-f64, load-u64): New instructions.

* module/language/bytecode.scm (compute-instruction-arity): Add parser
  for new instruction word types.

* module/language/cps/compile-bytecode.scm (compile-function): Add
  special-cased assemblers for new instructions, and also for scm->u64
  and u64->scm which I missed before.

* module/language/cps/effects-analysis.scm (load-f64, load-u64): New
  instructions.

* module/language/cps/slot-allocation.scm (compute-needs-slot): load-f64
  and load-u64 don't need slots.
  (compute-var-representations): Update for new instructions.

* module/language/cps/specialize-primcalls.scm (specialize-primcalls):
  Specialize scm->f64 and scm->u64 to make-f64 and make-u64.

* module/language/cps/types.scm (load-f64, load-u64): Wire up to type
  inference, though currently type inference only runs before
  specialization.

* module/language/cps/utils.scm (compute-defining-expressions): For some
  reason I don't understand, it's possible to see two definitions that
  are equal but not equal? here.  Allow for now.
  (compute-constant-values): Punch through type conversions to get
  constant u64/f64 values.

* module/system/vm/assembler.scm (assembler): Support for new word
  types.  Export the new assemblers.

module/language/bytecode.scm

@@ -51,8 +51,8 @@
     (case word
       ((C32) 1)
       ((I32) 1)
-      ((A32) 1)
-      ((B32) 0)
+      ((A32 AU32 AF32) 1)
+      ((B32 BF32 BU32) 0)
       ((N32) 1)
       ((R32) 1)
       ((L32) 1)