rework the vm support for wide strings

* libguile/_scm.h (SCM_OBJCODE_MINOR_VERSION): Bump.

* libguile/vm-engine.c (vm_error_bad_wide_string_length): New error
  case.

* libguile/vm-i-loader.c (load-unsigned-integer, load-integer)
  (load-keyword): Remove these instructions. The former two are
  obsoleted by make-int64/make-uint64, the latter via make-keyword.
  (load-string): Only handle narrow strings.
  (load-symbol): Only handle narrow symbols. The wide case is handled
  via make-symbol.
  (load-wide-string): New instruction, for wide strings.

* libguile/vm-i-system.c (define): Move here from loaders.c, as now it
  just takes a sym on the stack.
  (make-keyword, make-symbol): New instructions.

* module/language/assembly.scm: Remove removed instructions. No more
  width byte in load-string etc.

* module/language/assembly/compile-bytecode.scm (write-bytecode): Adapt
  to change in instruction set.

* module/language/glil/compile-assembly.scm (glil->assembly): Compile
  define by pushing the sym then emitting (define).
  (dump-object): Dump narrow and wide strings differently. Use
  make-keyword and make-symbol as appropriate.

* module/language/tree-il/compile-glil.scm (flatten): When compiling a
  ref to a primitive (not a call), first see if the primitive is
  actually bound in the root module. (That's not the case with e.g.
  bytevector-u8-ref).

* module/system/xref.scm (program-callee-rev-vars): Don't parse out
  "nexts".

* test-suite/tests/asm-to-bytecode.test ("compiler"): Adapt to bytecode
  format change.

libguile/vm-engine.c

@@ -220,6 +220,10 @@ VM_NAME (struct scm_vm *vp, SCM program, SCM *argv, int nargs)
     finish_args = SCM_EOL;
     goto vm_error;
 
+  vm_error_bad_wide_string_length:
+    err_msg  = scm_from_locale_string ("VM: Bad wide string length: ~S");
+    goto vm_error;
+
 #if VM_CHECK_IP
   vm_error_invalid_address:
     err_msg  = scm_from_locale_string ("VM: Invalid program address");