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mkrelease: fix three regressions, add simple 'dist' CI job #90

Job	Run time
Cygwin	2m 20s
Windows	42s
Linux (default, valgrind, test-memory)	3m 17s
macOS	15s
Linux (clang sanitizers, clang, test, clang, -fsanitize=address,undefined,signed-integer-overflow...	46s
	7m 20s

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