Move (back) missing functions in system libgd to gd_compat
- display libPng version in all cases
- gd_compat.c in ext/gd (nothing in ext/gd/libgd)
Merge branch 'PHP-5.5'

* PHP-5.5:
  Move (back) missing functions in system libgd to gd_compat - display libPng version in all cases - gd_compat.c in ext/gd (nothing in ext/gd/libgd)