Make the new printf-surprise test more precise.

Make the new printf-surprise test more precise.

* tests/test-lib.sh (require_ulimit_): New function.
* tests/misc/printf-surprise: Use ulimit -v to trigger the fixed bug,
and rather than checking printf's exit status (which would go wrong
on FreeBSD 6.1, since their printf(3) function doesn't require
lots of memory in this case) simply test whether it outputs
the first 10 bytes.