rust: fix signature of rustlazyancestors_init() function Obviously, sizeof(int) != mem::size_of::<usize>() on amd64, though the argument would be passed in 64-bit register anyway.

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# Avoid interference from actual test env:

unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL