[js] Make nqp::islist work properly on VMArray objects.

Author: pmurias

src/vm/js/Operations.nqp

@@ -845,7 +845,7 @@ class QAST::OperationsJS {
 
     add_simple_op('elems', $T_INT, [$T_OBJ]);
 
-    add_simple_op('islist', $T_BOOL, [$T_OBJ], sub ($obj) {"($obj instanceof nqp.NQPArray)"}, :decont(0));
+    add_simple_op('islist', $T_INT, [$T_OBJ], :decont(0));
 
 
 

src/vm/js/nqp-runtime/core.js

@@ -1068,3 +1068,7 @@ op.getlexref_n = function(hllName, get, set) {
 op.fc = function(string) {
   return string.toLowerCase();
 };
+
+op.islist = function(list) {
+  return (list instanceof NQPArray || list._STable && list._STable.REPR instanceof reprs.VMArray) ? 1 : 0;
+};