Fix spidermonkey AST (ESTree) export and import, Array holes

Fixes: #1156 #1161

Also add test to exercise Uglify after spidermonkey export/import of itself.

lib/mozilla-ast.js

@@ -94,6 +94,15 @@
                 return new AST_ObjectGetter(args);
             }
         },
+        ArrayExpression: function(M) {
+            return new AST_Array({
+                start    : my_start_token(M),
+                end      : my_end_token(M),
+                elements : M.elements.map(function(elem){
+                    return elem === null ? new AST_Hole() : from_moz(elem);
+                })
+            });
+        },
         ObjectExpression: function(M) {
             return new AST_Object({
                 start      : my_start_token(M),
@@ -206,7 +215,6 @@
     map("CatchClause", AST_Catch, "param>argname, body%body");
 
     map("ThisExpression", AST_This);
-    map("ArrayExpression", AST_Array, "elements@elements");
     map("FunctionExpression", AST_Function, "id>name, params@argnames, body%body");
     map("BinaryExpression", AST_Binary, "operator=operator, left>left, right>right");
     map("LogicalExpression", AST_Binary, "operator=operator, left>left, right>right");
@@ -302,6 +310,13 @@
         };
     });
 
+    def_to_moz(AST_Array, function To_Moz_ArrayExpression(M) {
+        return {
+            type: "ArrayExpression",
+            elements: M.elements.map(to_moz)
+        };
+    });
+
     def_to_moz(AST_Object, function To_Moz_ObjectExpression(M) {
         return {
             type: "ObjectExpression",