title: reverse function of require/include
body: <p>Is there any function that reverts a require/require_once/include/include_once?</p>
  
  <p>For instance in script A I need to require a script B wich has common functions witch other script C and I don't know if previously C was required or not. So I would like to "clean" script C from memory before loading B preventing duplicated functions.</p>