[Issue 6989] Implement toString for std.concurrency.Tid

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=6989

--- Comment #6 from Andrej Mitrovic <andrej.mitrovich at gmail.com> ---
(In reply to Sean Kelly from comment #5)
> Providing a provably unique
> identifier to each thread across the entire run of the program would be
> expensive.

Isn't starting a thread expensive enough that incrementing a simple counter
should be good enough to generate an ID?

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