Use 'batch' command line in gridsub

[Arnaud Malapert]

Use the batch/atd command in gridsub rather than simply launching sequentially shell scripts

• specify a limiting load factor, over which batch jobs should not be run, instead of the compile-time choice of 0.8. For an SMP system with n CPUs, you will probably want to set this higher than n-1.
• Setup the batch command in gridsub

We should also keep the serial submission mode.

[Arnaud Malapert]

or http://www.gnu.org/software/parallel/

[Arnaud Malapert]

or http://servforge.legi.grenoble-inp.fr/pub/soft-trokata/oarutils/oar-parexec.html

[Arnaud Malapert]

Finally, this is done by piping the output to the parallel command.
See commit 6bc7f87