Tweaks an add OPcache info to UPGRADING
Add SplDoublyLinkedList::add to UPGRADING
Note about bison version
Merge branch 'PHP-5.5'

* PHP-5.5:
  Note about bison version
  Add SplDoublyLinkedList::add to UPGRADING
  Tweaks an add OPcache info to UPGRADING

Conflicts:
	UPGRADING