Accepts as valid responses to staged requests. #439

Job	Run time
B2 msvc-14.2	4m 43s
B2 gcc-11	3m 18s
B2 msvc-14.3	5m 23s
CMake msvc-14.2 Debug C++17	6m 35s
B2 clang-14	3m 5s
CMake gcc-11 17 Debug	6m 8s
CMake msvc-14.2 Release C++17	6m 42s
CMake msvc-14.3 Debug C++20	6m 35s
CMake gcc-11 20 Release	7m 11s
CMake msvc-14.3 Release C++20	7m 37s
CMake clang-11 17 Debug	4m 11s
CMake clang-11 20 Debug	4m 13s
CMake clang-13 17 Release	5m 31s
CMake clang-13 20 Release	5m 48s
CMake clang-14 17 Debug -stdlib=libc++	6m 12s
CMake clang-14 20 Release -stdlib=libc++	7m 47s
	1h 30m 59s

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