Update to PHP-Parser 5.5.0 and add support for attributes on constants in
stubs. For now, I have only migrated over E_STRICT, once the support is in
place I'll do a larger migration of the existing deprecated constants.
In the process, fix the logic in `copy_zend_constant()` for copying attributes
when a constant is copied; just increase the reference count for the attributes
table rather than trying to duplicate the contents.
