Description:
------------
Various GMP Functions eat memory, when not called directly with integers or strings instead of gmp resources.

Reproduce code:
---------------
$a='1234';
for($i=0;$i<200000;$i++) {
  $c=gmp_add(gmp_init($a),gmp_init($a));
}
echo memory_get_usage() . "?\n";
for($i=0;$i<200000;$i++) {
  $c=gmp_add($a,$a);
}
echo memory_get_usage() . "?\n";


Expected result:
----------------
Both memory_get_usage() should show nearly the same values.

Actual result:
--------------
1732656?    // ~ 2 MB
43809696?   // ~ 43 MB