Fix iterator for PHP 5.5

Hi

Here is the fix for PHP 5.5, https://wiki.php.net/rfc/foreach-non-scalar-keys

With this fix applied, 

     =====================================================================
     TEST RESULT SUMMARY
     ---------------------------------------------------------------------
     Exts skipped    :    0
     Exts tested     :   17
     ---------------------------------------------------------------------

     Number of tests :   94                94
     Tests skipped   :    0 (  0.0%) --------
     Tests warned    :    3 (  3.2%) (  3.2%)
     Tests failed    :    0 (  0.0%) (  0.0%)
     Expected fail   :    0 (  0.0%) (  0.0%)
     Tests passed    :   91 ( 96.8%) ( 96.8%)
     ---------------------------------------------------------------------
     Time taken      :    3 seconds
     =====================================================================
     
     =====================================================================
     WARNED TEST SUMMARY
     ---------------------------------------------------------------------
     Test for iterating over a hash while adding/deleting entries through ArrayAccess. [tests/int-hash-iterator3.phpt] (warn: XFAIL section but test passes)
     Test for iterating over a hash while adding/deleting entries through ArrayAccess. [tests/int-string-hash-iterator3.phpt] (warn: XFAIL section but test passes)
     Test for iterating over a hash while adding/deleting entries through ArrayAccess. [tests/string-int-hash-iterator3.phpt] (warn: XFAIL section but test passes)
     =====================================================================