Merge PHP RFC: Closure::call

Commits:
  NEWS, UPGRADING
  Fixed Closure::apply() for int64
  Just return, no need for RETURN_NULL()
  Revert "Fixed closure::bindTo bad args test"
  Accuracy
  Fixed issues spotted by code review
  Comment clarification
  Old comment, whitespace
  Don't allow unbound scoped closures; make ->call used passed object as scope
  Removed unused variable
  Fixed and cleaned up implementaton of Closure::call() for phpng
  Fixed closure::bindTo bad args test
  Fixed unbound scoped closure edge cases and added tests for them
  Rename ::apply to ::call for the sake of JS consistency
  Added test for unbound_scoped
  Added optional bool param $unbound_scoped to Closure::bind and ::bindTo
  Implemented Closure::apply