Fix bug #62759: Buggy grapheme_substr() on edge case
Merge branch 'PHP-5.4' into PHP-5.5

* PHP-5.4:
  Fix bug #62759: Buggy grapheme_substr() on edge case
Merge branch 'PHP-5.5'

* PHP-5.5:
  Fix bug #62759: Buggy grapheme_substr() on edge case