Description:
------------
It seems that zval_ptr_dtor doesn't check if strings are heap-allocated.

Reproduce code:
---------------
// Change this to zero to get a SEGV
int heapAllocate = 1;

// Make a string zval
zval* v;
MAKE_STD_ZVAL(v);
ZVAL_STRING(v, "foo", heapAllocate);

// SEGV happens here
zval_ptr_dtor(&v);

Expected result:
----------------
Nothing.

Actual result:
--------------
php-5.3.0/Zend/zend_execute_API.c(435) : Block 0x004014fa status:
php-5.3.0/Zend/zend_variables.c(36) : Actual location (location was relayed)
Invalid pointer: ((thread_id=0x74706972) != (expected=0x96F6B8A0))