Description:
------------
* memory leak in version 7.0+ (7.0.22 from repository ubuntu 16.04; 7.1.5 from sources, minimal configuration)

Test script:
---------------
$a = array();
for ($j = 1; $j <= 3; $j++) {
  for ($i = 0; $i < 50000; $i++) {
    $a[] = range(0, 10);
  }
  echo "Memory: ", (memory_get_usage(true) / 1024), " KiB\n";
  $a = null;
  unset($a);
  $a = array();
  echo "Memory: ", (memory_get_usage(true) / 1024), " KiB\n";
}

Expected result:
----------------
Memory: 92160 KiB
Memory: 768 KiB
Memory: 92160 KiB
Memory: 768 KiB
Memory: 92160 KiB
Memory: 768 KiB

Actual result:
--------------
Memory: 36868 KiB
Memory: 34816 KiB
Memory: 36868 KiB
Memory: 34816 KiB
Memory: 36868 KiB
Memory: 34816 KiB