Description:
------------
When PHP first introduced visibility, it did not yet have namespaces, so the only applicable visibility schemes were related to classes -- members were either global (public), or local to the class (private), possibly including parents and children (protected).

But with the addition of namespaces, there is now a need for a visibility scope between public and protected.  Developers (like me) will use namespaces to create packages -- collections of classes that are meant to work closely with each other.  In this context, it would be very convenient to be able to make members visible to other (unrelated-by-inheritance) classes within the same package (namespace), but hidden from the world outside the package.

Since the 'namespace' keyword is currently only allowed on the first line of a file, and therefore could not occur inside a class, I suggest re-using it for this purpose rather than introducing another reserved word.

Reproduce code:
---------------
<?php
namespace Test;
class A {
  namespace static $nsVar = 'Test::A::nsVar';
  static function test() {
    echo __CLASS__." can see ".A::$nsVar."\n";
  }
}
class B {
  static function test() {
    echo __CLASS__." can see ".A::$nsVar."\n";
  }
}
Test::A::test();
Test::B::test();


Expected result:
----------------
Test::A can see Test::A::nsVar
Test::B can see Test::A::nsVar


Actual result:
--------------
(syntax error on 'namespace', line 4)