Fix exit status of signal handlers in shell scripts. The value of `$?' on entrance to signal handlers in shell scripts cannot be relied upon, so set the exit code explicitly to 128 + SIG<SIGNAL>. * lib/am/check.am (am__check_pre): Use `exit 143' in signal handler. * lib/elisp-comp: Likewise. * lib/install-sh: Likewise. * lib/ylwrap: Likewise. Also, fix script to trap signal 13, not 3. * NEWS, THANKS: Update. Bug report, analysis, and initial patch by Dmitry V. Levin. Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>