fix bugs with getter/setter (#1926)

- `reduce_vars`
- `side_effects`
- property access for object
- `AST_SymbolAccessor` as key names

enhance `test/ufuzz.js`
- add object getter & setter
  - property assignment to setter
  - avoid infinite recursion in setter
- fix & adjust assignment operators
  - 50% `=`
  - 25% `+=`
  - 2.5% each for the rest
- avoid "Invalid array length"
- fix `console.log()`
  - bypass getter
  - curb recursive reference
- deprecate `-E`, always report runtime errors

lib/scope.js

@@ -361,11 +361,6 @@ AST_Symbol.DEFMETHOD("unmangleable", function(options){
     return this.definition().unmangleable(options);
 });
 
-// property accessors are not mangleable
-AST_SymbolAccessor.DEFMETHOD("unmangleable", function(){
-    return true;
-});
-
 // labels are always mangleable
 AST_Label.DEFMETHOD("unmangleable", function(){
     return false;