Deprecate `save` for `std.range.package.Transposed`

Transposed is incorrectly marked as a forward range. Its `popFront` primitive
cannot be used without affecting any other copies made with `save`. `save` will be
removed from Transposed in November 2018.

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auto x = [[1,2,3],[4,5,6]].transposed;
auto y = x.save;
y.popFront;
assert(x.equal([[1,4],[2,5],[3,6]])); // FAILS, x is really [[2,5],[3,6]]
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For more details, please see the respective $(LINK2 https://issues.dlang.org/show_bug.cgi?id=17952,
Bugzilla issue).