Sync with pecl/zip 1.12.4dev

- update bunled libzip to 0.11.2
- expose zip_file_set_external_attributes + zip_file_get_external_attributes
  with new methods:
	ZipArchive::setExternalAttributesName
	ZipArchive::setExternalAttributesIndex
	ZipArchive::getExternalAttributesName
	ZipArchive::getExternalAttributesIndex
Merge branch 'PHP-5.6'

* PHP-5.6:
  Sync with pecl/zip 1.12.4dev