check: indicate the test failures with non-zero exit code; split test programs.

check: indicate the test failures with non-zero exit code; split test programs.

IMNSHO parsing the output of test programs in order to check if the
tests passed is a bad idea (and it causes *real* problems, see e.g.
http://www.ginac.de/pipermail/ginac-list/2008-February/001345.html).
It's much simpler and cleaner to indicate the failure in a genuine
*NIX way: exit with nonzero code.