Disable test cleanup trap with OSF1/Tru64 sh.

Disable test cleanup trap with OSF1/Tru64 sh.

* configure.ac: Test whether /bin/sh has working 'set -e'
in conjunction with an exit trap.  Set $am_cv_sh_errexit_works
accordingly, substitute sh_errexit_works, and warn about
leftover test directories with broken shells like Tru64 /bin/sh.
* tests/defs.in: Do not install any traps with broken shells.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>