What's the deal with __thread?

[Don Clugston]

IIRC it was used prior to 2.030. In the spec, it is in the keyword list, 
and it's also listed in the "Migrating to shared" article. That's all. 
There are a small number of uses of it in the DMD test suite.

Is it still valid? Is it useful? Or has everyone forgotten that it still 
exists?