Module_implements refresh is not working

In module_implements function in module.inc when refresh is true we try to delete all previous values in $implementations but because $implementations is static we can't do that with unset. Quote from php docs http://www.php.net/manual/en/function.unset.php

If a static variable is unset() inside of a function, unset() destroys the variable only in the context of the rest of a function. Following calls will restore the previous value of a variable.

My patch does that with
$implementations = array();