Issue 6224 - Add ownerTid() property.

http://d.puremagic.com/issues/show_bug.cgi?id=6224

Nothing too controversial. But since the returned type is a struct I figure it's better to throw an exception rather than the user getting a segfault when they try to call `ownerTid.send()`.

Additionally I've removed `Tid.send`, it was duplicated code but isn't required anymore since UFCS can take its place.