Add test for issue 486

[clairetaylor352]

Adds test for #486

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[clairetaylor352]

@googlebot I signed it!

[adetaylor]

println needs zapping

[adetaylor]

It's possible that the test will pass if you change this line to inline bool b(a::spanner::Key &) {}

[adetaylor]

Actually no it won't, the problems seem to be genuine problems confusing Key and spanner::Key

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