Use reinterpret cast is [does|may]PointTo

Instead of a straight up cast. Avoids problems related to opCast or alias this, such as those in:
http://forum.dlang.org/thread/vldwvnuivsfwjozqiuup@forum.dlang.org
Is this correct? For some reason, `alias opCast!(void*) this` does not work. The `alias this` syntax may only alias a single *token*, correct? Kind of weird...