Add ensemble mean value to the ORANK line type from ensemble_stat.

[dwfncar]

Add the ensemble mean value to the end of the ORANK line type produced by ensemble_stat. This is needed for the gsidens2orank tool. By having a spot to write the ensemble mean value to that line type, we'll be able to enhance stat_analysis by defining an aggregate_stat job for ORANK -> SSVAR. That means that the gsid2ens2orank tool won't need to compute SSVAR itself.
[MET-530] created by johnhg

[dwfncar]

Added ensemble mean to the end of the ORANK line type and enhance STAT-Analysis to aggregate ORANK line types and write SSVAR.
by johnhg