primitives: add scope

[WalterBright]

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[dlang-bot]

Thanks for your pull request, @WalterBright!

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[wilzbach]

std/range/primitives.d(600): Error: `@safe` function `std.range.primitives.__unittest_L593_C7` cannot call `@system` function `std.range.primitives.put!(int[][], int[]).put`
std/range/primitives.d(610): Error: `@safe` function `std.range.primitives.__unittest_L605_C7` cannot call `@system` function `std.range.primitives.put!(int[][], int[]).put`

Maybe we should be a bit more careful with this one?

[n8sh]

As this is just replacing in with scope const inside some unit tests (and the two were at one point intended to by synonymous), if the tests were passing before this PR and are still passing after it I don't see a reason not to merge this.

[wilzbach]

rebased to master