pgsql: If pg_ctl stop fails, print an error message and exit (instead of

Log Message:
-----------
If pg_ctl stop fails, print an error message and exit (instead of going out
of our way to ignore the exit status). If this ever really happens, worst
case you will not see the "score" at the bottom of the test run.

Modified Files:
--------------
pgsql/src/test/regress:
pg_regress.c (r1.50 -> r1.51)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/pg_regress.c?r1=1.50&r2=1.51)