Added infrastructure to support allocation of generic node resources.

    -Added node configuration parameter of Gres=.
    -Added ability to view/modify a node's gres using scontrol, sinfo and sview.
    -Added salloc, sbatch and srun --gres option.
    -Added ability to view a job or job step's gres using scontrol, squeue and
     sview.
    -Added new configuration parameter GresPlugins to define plugins used to
     manage generic resources.
    -Added framework for gres plugins.
svn merge -r20080:20102 https://eris.llnl.gov/svn/slurm/branches/slurm-2.2.gres (NOT BRANCH 2.1)