averagePlotfile - Create a pltfile by averaging existing pltfiles

Two tools exist for the purpose of averaging plotfiles. averagePlotfile assumes all plotfiles to be averaged have the same underlying BoxArrays, or the output is only given at the base level. averagePlotfileFlexible relaxes this assumption: the output file will be refined anywhere any of the input files are refined (coarse data is interpolated to the finer levels in each file as needed before averaging to obtain this result). Both tools require that all files have the same domain and base grid, and by default the same variables. averagePlotfileFlexible adds the capability to optionally select a specifc list of variables, in which case that list must be present in all input files but otherwise the input files may contain different sets of variables.

``` Usage:

./avgPlotfilesFlexible2d.gnu.MPI.ex infiles=$(ls -d plt*) [options]

```

Example: