Spurious failures in test_cookie_str_changed_mac
(originally https://github.com/martinpaljak/M2Crypto/issues/70)
@mitr: The test tests that a modification of MAC is detected by replacing one character by 'X', but from time to time the original MAC may have an 'X' in that place, in which case the modification doesn’t happen.
The patch ensures that the cookie is really modified; the other two tests are structurally similar and have the same fundamental problem in principle, but it is unlikely (or impossible?) for them to have the same value; still, the patch modifies the others as well for reliability and consistency.
Fix in https://github.com/martinpaljak/M2Crypto/pull/71 which is now https://gitlab.com/mcepl/m2crypto/commits/spurious_cookie_failures