need check for npes > ni, nj

[StephenGriffies]

There should be an "idiot" check for the case where npes is greater than the number of grid points in the model. For example, with the SCM tests, the model crashes when npe>1, but there is no error message that tells the user what went wrong. It is obvious after-the-fact, but for new users (e.g., Griffies), it would prove very useful to have this sort of error message, particularly since the example run command on the wiki has "aprun -n 8".