[Issue 6587] std.parallelism's Task cannot handle immutable values

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=6587
Issue 6587 depends on issue 6588, which changed state.

Issue 6588 Summary: Struct d'tors + immutable elements doesn't work
https://issues.dlang.org/show_bug.cgi?id=6588

           What    |Removed                     |Added
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             Status|NEW                         |RESOLVED
         Resolution|---                         |WORKSFORME

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