[svn-r21459] Problem:

Some machines, like LLNL udawn, a blue-gene machine, requires all executables,
be launched by some command like mpirun.

Solution:
Added $RUNSERIAL to launch the executable.

Tested: LLNL uDawn.

test/testlinks_env.sh.in

@@ -35,7 +35,7 @@ TEST_BIN=`pwd`/$TEST_NAME 	# The path of the test binary
 ENVCMD="env HDF5_EXT_PREFIX=.:tmp" 	# The environment variable & value
 #
 # Run the test
-$ENVCMD $TEST_BIN
+$ENVCMD $RUNSERIAL $TEST_BIN
 exitcode=$?
 if [ $exitcode -eq 0 ]; then
         echo "Test for HDF5_EXT_PREFIX PASSED"