Show name of NYI bytecode in -jv and -jdump.

Suggested by Sergey Kaplun. #1176 #567

src/jit/dump.lua

@@ -552,7 +552,12 @@ local recdepth = 0
 local function fmterr(err, info)
   if type(err) == "number" then
     if type(info) == "function" then info = fmtfunc(info) end
-    err = format(vmdef.traceerr[err], info)
+    local fmt = vmdef.traceerr[err]
+    if fmt == "NYI: bytecode %s" then
+      local oidx = 6 * info
+      info = sub(vmdef.bcnames, oidx+1, oidx+6)
+    end
+    err = format(fmt, info)
   end
   return err
 end