tests: prefer ulimit over timeout in test on a memory-hogging bug

tests: prefer ulimit over timeout in test on a memory-hogging bug

* tests/cond29.test: Use 'ulimit' instead of 'timeout' to ensure
that automake does not uses up too much resources.  This is really
and improvement because the bug tested by this script wasn't just
a "it hangs" or "it runs too slow" bug, but rather a memory-hogging
bug (due to combinatorial explosion when many Automake conditionals
had to be handled) which could easily crash the whole system, which
is unacceptable.  The requirement of a proper and working 'ulimit'
builtin might cause the test to be skipped on more systems, but
that shouldn't be a problem since the bug isn't about a portability
issue, but is rather an automake internal implementation problem.
I've verified that the test as updated by this patch still passes
with automake 1.8.5, automake 1.10.2, and obviously the development
version of automake, and that it fails with automake 1.7.9.