Bug 19596 – Docs on .walkLength are wrong

https://dlang.org/phobos/std_range_primitives.html#walkLength "This is a best-effort implementation of length for any kind of range." This statement from the docs is not true. walkLength (and probably some other functions) do not work for a range with @disable'd copy constructor. So it is not "for any kind of range" as claimed in the docs. Correct either the code to conform the docs or the docs.

You cannot pass a non-copyable struct to a function by value. There is little point in advertising this fact in the docs for every function that can possibly accept a user-defined struct. It's something you have to know when you use this feature. Pass a pointer to the range instead.