Improve and extend test cond5.test.

Improve and extend test cond5.test.

* tests/cond5.test: Do not blindly sleep 60 seconds before polling
the background automake process, but poll it every 10 seconds for
at most 30 times (this makes the test both faster on good machines,
and more resilient to spurious timeout-due failures when in low
priority or on havily-loaded systems).
Check also that automake writes the expected error messages on the
standard error.
Enable `errexit' flag, and related changes.
Rely on the `configure.in' stub created by `./defs', rather than
writing one from scratch.