tap/awk: account for unusual korn shell signal handling behaviour This change has been motivated by a testsuite failure on Debian with the AT&T Korn Shell version 93u-1. * lib/tap-driver.sh: Temporarily ignore some common signals when waiting for the test command to complete, to avoid premature exit in Korn shells that propagate to themselves signals that have killed a child process. See also related commit `v1.11-1342-g6321ad3'.