As it turns out, there is actually no reason to prevent this, it even was a bigger BC break than expected...
Also fixes a memory leak (the Closure leaks) when calling internal functions via Closure by moving it out of leave helper onto caller side for TOP_CODE:
$z = new SplStack; $z->push(20);
$x = (new ReflectionMethod("SplStack", "pop"))->getClosure($z);
var_dump($x());
Now it is completely impossible to rebind a scoped method Closure (only the kind you get from ReflectionMethod::getClosure()) to a foreign scope
Adding a lot of tests to ensure this...
Also, properly return NULL in case the Closure could not be created instead of some crippled unbound Closure
This additionally removes support for binding to an unknown (not in parent hierarchy) scope.
Removing support for cross-scope is necessary for certain compile-time assumptions (like class constants) to prevent unexpected results
