Added prototype for a simple cache layer

Right now it caches the objects by ID.
minor change
Merge branch 'release/v0.1.7' into develop
fixed minor bug
fixed minor bug
Calling private/protected methods
Improve References of references

It was generating fatal error when a Reference has another reference cached
Merge branch 'develop' into feature/simple-cache

Conflicts:
	lib/ActiveMongo2/Connection.php
Merge branch 'feature/simple-cache' into develop
Added Connection::setCacheStorage to change the storage on the fly
Added Cursor::getResultCache()

This function will return an array of raw documents that can be stored in your favorite cache database (I bet Redis :P). Collection::resultCache(Array $) can populate it back and it would be as if the results came from MongoDB.
minor fix
fixed issue with mapping dynamic documents
improved exception
Parent classes should be accesed by name not by class
Improved @GridFS files population after save
Improved Cache Iterator
Improved CacheReference of referecens
minor change
Fixed @Password rehashing issue