reduce arguments by reference #14
Description
This PR reduces arguments by reference often used on internal methods.
It was previously done as performance improvement but in fact it decreases performance as PHP have to create a new zval and in some cases it needs to copy the value before PHP-7 as described here: http://nikic.github.io/2015/05/05/Internal-value-representation-in-PHP-7-part-1.html
Additionally arguments by reference make the code more error prone and hard to read.
Originally posted by @marc-mabe at zendframework/zend-cache#8