Use zval_ptr_dtor() to free variables as soon as they hit refcount of 0.

Use zval_ptr_dtor() to free variables as soon as they hit refcount of 0.

Note:  You should not be using ZVAL_DELREF() in day to day usage.  Instead,
       you should use zval_ptr_dtor().  Use ZVAL_DELREF() only if you're
       messing with the refcount directly and know what you're doing.
Note #2:  For clarity, if you want to initialize a new zval with a refcount
          of 0, it's best to do that directly, instead of using ZVAL_DELREF
          after allocating the zval...