lambda-lifting for (lambda () ...) as consumer of call-with-values

* libguile/vm-engine.c (vm_run): Add new error case,
  vm_error_not_enough_values.

* libguile/vm-i-system.c (goto/nargs, call/nargs): So, in these cases, if
  we get too many values, we don't truncate the values like we do in the
  single-value continuation case, or in the mvbind case. What to do? I
  guess we either truncate them here, or only allow the correct number of
  values. Dunno. Mark the code as a fixme.
  (truncate-values): New instruction, for mv-bind: checks that the number
  of values on the stack is compatible with the number of bindings we
  have arranged for them, truncating if necessary.

* module/language/scheme/translate.scm (custom-transformer-table):
  Compile receive as a primary form -- not so much because it is a
  primary form, but more to test the mv-bind machinery. Also it's more
  efficient, I think.

* module/system/il/compile.scm (lift-variables!): New helper, factored
  out of `optimize'.
  (optimize): Add a few more cases. Adapt `lambda' optimization, which
  isn't much. I'm not happy with ghil as a mungeable language.
  Add a case for call-with-values with the second argument is
  a lambda: lift the lambda. Untested.
  (codegen): Refactor the push-bindings! code. Compile mv-bind.

* module/system/il/ghil.scm (<ghil-mv-bind>): Add mv-bind construct,
  along with its procedures.

* module/system/il/glil.scm (<glil-mv-bind>): Add mv-bind construct,
  different from the high-level one. It makes sense in the source, I
  think.

* module/system/vm/assemble.scm (codegen): Assemble glil-mv-bind by
  pushing onto the bindings list, and actually push some code to truncate
  the values.

libguile/vm-i-system.c

@@ -713,6 +713,7 @@ VM_DEFINE_INSTRUCTION (goto_nargs, "goto/nargs", 0, 0, 1)
   SCM x;
   POP (x);
   nargs = scm_to_int (x);
+  /* FIXME: should truncate values? */
   goto vm_goto_args;
 }
 
@@ -721,6 +722,7 @@ VM_DEFINE_INSTRUCTION (call_nargs, "call/nargs", 0, 0, 1)
   SCM x;
   POP (x);
   nargs = scm_to_int (x);
+  /* FIXME: should truncate values? */
   goto vm_call;
 }
 
@@ -963,6 +965,29 @@ VM_DEFINE_INSTRUCTION (return_values_star, "return/values*", 1, -1, -1)
   goto vm_return_values;
 }
 
+VM_DEFINE_INSTRUCTION (truncate_values, "truncate-values", 2, -1, -1)
+{
+  SCM x;
+  int nbinds, rest;
+  POP (x);
+  nvalues = scm_to_int (x);
+  nbinds = FETCH ();
+  rest = FETCH ();
+
+  if (rest)
+    nbinds--;
+
+  if (nvalues < nbinds)
+    goto vm_error_not_enough_values;
+
+  if (rest)
+    POP_LIST (nvalues - nbinds);
+  else
+    DROPN (nvalues - nbinds);
+
+  NEXT;
+}
+
 /*
   Local Variables:
   c-file-style: "gnu"