Revert "PersistentCollection::count() with ReferenceMany InverseSide mapping queries DB without collection initialization"

This reverts commit bd7d99e290159e310469b0a14aee1aafc7df2381.

Conflicts:
	lib/Doctrine/ODM/MongoDB/PersistentCollection.php

Reverting, because not initializing counted incorrectly when:
	- the collection has the isInverseSide flag set
	- the collection is uninitialized
	- has had an item added using add(), making it dirty

Here's the previous (and broken before this commit) flow:
	- the collection is inverse-side and not initially initialized
	- we add an item via add()
		- has the side-effect of marking the collection as dirty
		- but still keeps the collection uninitialized
	- if count() is called now for this uninitialized inverse-side collection:
		- a query gets sent to the database to count the objects
		- the result of counting is 0, because:
			- there's nothing in the DB yet
			(assuming there really was nothing old there for starters)
			- nobody cared that $this->coll had some items added to it
			and the collection was dirty

The easiest fix I can think of is to restore the old behavior, which
causes initialize() to happen just in case.