Added test for PHP-735
We need to apply the RP set on the _cursor_ not MongoClient here

This fixes issues where RP set on db/collection/cursor/whatever not
being properly sent over to mongos
Fixed PHP-735: Commands should inherit ReadPreferences from MongoDB and MongoCollection objects
Fix teset after PHP-735 fix (actually setting the slaveokay flag!)
Remove now unused argument
zval *query is no longer needed either.
Merged pull request #386